The hitbox is the simplest of ways to detect collisions. There are plenty of terms used for it, and it does not always take the form of a “box” anymore (3D games, but hitbox is the term I’ve grown to know and love, and I’m sticking to it. The Japanese term is hantei, literally meaning “judgement”; while this umbrella term aligns a bit better with what hitboxes do, it is a bit more confusing.
The term (just like the Japanese etymology) comes from the development side of computer programming. Hitboxes make it simple to determine whether two things are touching; instead of making a lot of tests to determine an overlap of sorts, the programmers only need to test the corners of the boxes, saving a lot of computational power. This “cheat” has been exploited since the halcyon days of old-school action gaming, and will not be disappearing in the foreseeable future.
The name itself just implies that boxes are touching. It applies whether it is the box doing the hitting, or the box getting hit.
Hitboxes are not visibly apparent when you play (if they were, they wouldn’t doing their job right, which is to give the illusion that something is happening just like in the physical world). They are a concept internal to the program, but understanding them enhances your knowledge of the game.
Separately from the graphics, hitboxes determine where your character is to the game’s internal mechanics. They keep track of spaces, parts, things, characters... and they are the manifestations of special states.
The short of it is that when hitboxes touch, reactions happen. An attack hitbox manifests an attack’s location; if there is a damage hitbox on the receiving end right there, then regardless of where the opponent’s body is, they will take that attack. If there isn’t one (like, say we had an “invincible hitbox”), then the attack will miss as if the opponent weren’t there, even if they are.
In Japanese, the overhead hitbox is chūdan hantei, meaning “mid-level hitbox”. This gets confusing in places, particularly for the native speakers. This line of thinking stems from the idea that a “high” hitbox would go above overhead level, especially when someone is crouching; however, the term jōdan hantei (“high-level hitbox”) more often refers to a strike that may be blocked standing or crouching (though this definition changes from game to game), which oddly enough, is generally lower than overhead level.
In English, the differentiation between different-“height” hitboxes (which are not truly height-based so much as related to statuses) does not generally have a standard set of terms beyond “overhead” and “low” (not the least of which is caused by different behaviors in different games). Please bear this in mind while reading my articles; I attempt to maintain my own continuum of terms, but they are by no means an accepted, widely-used set. This goes for any set of terms on this site, actually, but in this section, even more so.
Below are the main types of the many kinds of hitboxes.