This is an open thread (so to speak) so we can define what we understand as a martial art. The "best" answer should probably go to the FAQ.
Linked question: Do we need to define martial art?
Please edit to whittle away chaff and include the information necessary for the purposes of this site. Based on @BobCross's wiki reprint:
Martial arts are
extensivesystems of codified practices and traditions of combat that are practiced for a variety of reasons, includingself-defense, competition, physical health and fitness, as well as mental, physical and spiritual development.
Please clean up and alter as necessary.
Removed "extensive" to be inclusive of rather limited systems (Uchida-ryu Tanjojutsu is a martial art, but extremely limited in scope).
Removed "a variety of reasons" to prevent too broad of a definition.
Bob: I moved the strike tag slightly. Personally, I would also consider removing "as well as mental, physical and spiritual development" - that phrase is too loosely defined. The result would then be:
Martial arts are systems of codified practices and traditions of combat that are practiced for self-defense, competition and fitness.
The first sentence of the Wikipedia entry is a reasonable starting place:
Martial arts are extensive systems of codified practices and traditions of combat that are practiced for a variety of reasons, including self-defense, competition, physical health and fitness, as well as mental, physical and spiritual development.
EDIT: keep in mind that it is sometimes easy to come up with negative examples. For instance, we could list things that are definitely off the table: e.g., Taebo, WWE, stage combat and others that try to add a thin martial arts flavor.
Coming out from a discussion with @stslavik, I propose something like this:
"Martial arts" refer to both the arts with the single purpose of prevailing in a physical conflict (e.g. not debate) and the arts which are, in short, a "way of life". The latter are slightly trickier to define, since their influence extends to just about every aspect of living one's life, including but not limited to mental processes, social interactions and relations to the spiritual. Meditation, Qigong (chikung) and breathing exercises are all included in the recipe - as well as, of course, self-defense.
If Qigong and breath work are included, the door is almost open to Chinese Medicine - some movements and sequences of movements specifically activate / disable points on meridians (health / defense) and have various repercussions. Where do we draw the line?
Online etymology dictionary has some etymological sources as to the martial part with [...]martialis "of Mars or war[...]". Thus I would define a martial art as a performance of movements those origins can be traced to war.
"Martial art is the practice of combat. It is practiced for sport as in boxing or judo, for the military or law enforcement as in hand-to-hand combat training or handcuffing techniques, or for recreation, health and physical culture. Martial arts necessarily involve the practice of some aspect of fighting: striking, grappling, and/or the use of weapons."
Some interesting discussion here. I know, I subscribe to a very unpopular notion that much of what we practice is not martial arts at all - anything we do in a dojo, a tatami mat, or a gym is not martial arts - boxing, wrestling, taekwondo, aikido, qigong...
Martial means "of, or about, war" - and arts is loosely defined as the application (a product of human creation) of that which is of or about war.
In all these definitions, we mention things like fighting, combat, and even war - but then there must be assumptions about what those terms mean as well, and so, there still isn't any accord on what is "martial art".
Take war, for example - the very basis for the word "martial". Does it require fighting? I posit that it doesn't have to. War on terror. War on drugs. Cold war. The Pig War. The War of Iceland (aka, the Invasion of Iceland). The war we are currently fighting North Korea this very day - it's legally a war. Most of these wars have very little fighting, and some with no casualties. Much of it involves politics, covert surveillance, training, strategy, change of lifestyle, negotiations... not just fighting (whatever that means).
War is all about a nation meeting the aggression of another - usually in a very forceful way. But it also involves negotiation, trade sanctions, bargaining, threats. It also means battlefield survival, navigation, communication, and allying with others.
And what about that fighting? It's surely not about a match between two unarmed participants fighting when told to start and end with a bell or referee. It's about unfair tactics, many-vs-many, and armed to the teeth. It involves more about weapons than anything hand-to-hand. Never has a modern war been won on the basis of hand-to-hand fighting alone - weaponry is nearly always the deciding factor.
So why do we take that tiny little element - hand-to-hand fighting - and call it martial arts? That tiny little element of hand-to-hand fighting is even tinier because we even limit what we are allowed to do when we engage: boxing has no grappling, wrestling has no strikes, and none allow weapons. Why do we call these things "martial arts"?
If we are going to take a micro-element of war - tiny parts of hand-to-hand fighting - and call it martial arts, why not take other micro-elements of war and call it martial arts? Like, first aid? (Oh, wait a minute, we already did that. Qigong is about healing, yes? So Qigong must be a martial art?)
Why some say Qigong not a martial art while wrestling is?
I could go on and suggest cooking is a form of martial art, because, everyone in war needs to eat, and there are those in the military whose job it is to prepare that food. And a bugler and drummer, they were an important part of battlefield communication. Should a bugler be considered a martial artist? No? Why not? They also fight, yes?
Now, I am not suggesting that chefs, buglers, doctors, chaplains, motor pool specialists, radio repairmen, and war photographers are all martial artists, although I struggle to find a logical reason why not, since these jobs are integral functions of war management.
And about war management: aren't generals and admirals martial artists, since they are the war's strategists? They're the ones employing the weaponry. Why do we not refer to them as "martial artists" even though they make or break a war's or battle's outcome?
It makes so little sense to me to cherry pick things "of or about war".
And I struggle to understand why we call Taekwondo - with all of its padding and electronic scoring and limited techniques and targets - a "martial art". No soldier ever donned such padding - although perhaps the plate mail, chain mail, or leather mail is a logical analogy to the modern day padding. But the purpose of today's padding is to protect both the attacker and the defender, whereas the mail worn in the old days was meant only to protect the wearer. And that e-scoring thing?
And I struggle to understand why we call boxing - with no protection at all other than gloves and a boundary where the fight is supposed to occur - a "martial art". What soldier ever put on balloon shaped gloves and engaged an enemy wearing shorts and sneakers?
None of the fighting we do in any dojang, tatami mat, or gym has any relation to war or battles - land, sea, or air. So why do we refer to them as "martial arts"?
I got sort of directed here by reading discussion on why wrestling is a martial art, and tried to figure out what the community decided defines martial arts, and this discussion didn't seem to come to any conclusion - even after 6 years. Maybe a debate (a fight?) is in order, but I doubt there will be agreement. The accepted answer "Martial arts are systems of codified practices and traditions of combat that are practiced for self-defense, competition and fitness" seems to cover only a small portion of the practices of combat. IMHO.