Invincibility, as the name suggests, is the inability to be hit by, or receive damage from, an attack. It is a common attack property in many fighting games, including M.U.G.E.N.
Characters with full invincibility are unable to be hit by any attack, throw, or projectile. In addition to full invincibility, many forms of partial invincibility exist.
Projectile Invincibility renders the character immune to projectile attacks, but can still be hit by throws and physical attacks. Projectile Invincibility may or may not be accompanied with the ability to nullify projectiles as well. The most common attack that posses Projectile Invincibility is the Tatsumaki Senpuukyaku (Hurricane Kick), known by many Shoto-clone characters such as Ken Masters and Ryu.
A specialized form of Projectile Invincibility known as Graze exists in the Touhou Project series. In the Touhou fighting games, grazing provides the player with the ability to cancel or nullify certain enemy projectiles simply by running, dashing, or super jumping into them, or with the use of certain special moves, and ends as soon as the player leaves the state with graze properties. Unlike normal projectile invincibility, grazing will also provide the property against certain projectiles.
Startup Invincibility grants the character with full invincibility, but only during the startup frames of an attack. Startup invincibility may or may not extend into the active frames of an attack, depending on the attack with this property. It is a common property of reversal attacks, such as the Shoryuken.
Upper/Lower Body Invincibility
As the name implies, this type of invincibility only grants invincibility on specific parts of the character's body. Upper Body invincibility grants immunity to most attacks, while Lower Body invincibility grants immunity to most attacks. In many fighting games, including M.U.G.E.N, these types of invincibility are accomplished with clever hitbox placement, rather than declaring invincibility through a special property (such as M.U.G.E.N's NotHitBy state controller). In many fighting games, most jumping states have Lower Body invincibility by default, including aerial attacks.
This type of invincibility renders the character immune to grabs and throws, but can still be hit by physical attacks and projectiles. By default, all airborne and jumping states, including the jump startup where the character is still on the ground, have immunity in most fighting games; however, this only applies to ground throws. Likewise, all grounded states have throw immunity to attacks. Immunity to both and attacks are usually only seen in many large boss-type characters, such as Abyss and Apocalypse. It is also a common property of some Command Grab specials.