Pushbox
The collision box that stops two characters from standing on the exact same spot — the thing that shoves them apart when they bump.
Fighting games juggle several invisible shapes per character. Alongside the hitbox (the damaging region) and the hurtbox (the vulnerable one) sits the pushbox, which neither deals nor takes damage. Its only job is to refuse to overlap another pushbox: when two fighters walk into each other, they get pushed apart.
The shape is almost always a simple rectangle around the torso, often narrower than the sprite looks. Its width decides how "sticky" bodies feel, why you get stuck in a corner, and whether a cross-up lands on the correct side. The designer tunes it independently of the art, exactly as with the hitbox — what you see is rarely what counts.