A Reflection is the process of deflecting incoming projectiles. The projectile then becomes property of the reflector's user and is often redirected to hit the original attacker, though some moves such as Thunder are not redirected when reflected. Most reflectors increase the damage done by projectiles, while some also increase their speed. Projectiles can be reflected from any direction.
It is possible for a single projectile to be reflected multiple times, such as back and forth between two characters' reflectors. However, this cannot be kept going indefinitely as all reflectors cannot withstand a projectile that becomes too powerful: a very strong projectile just passes through most reflectors, while actually physically shattering others (such as Guardian Orbitars and Reflect Barrier).
Moves with reflecting abilities
* In Melee, Confusion simply reverses projectiles without changing their owner.
In SSB64 and Melee, if a projectile is too strong for a reflector, the reflector breaks and stuns its user. In Brawl and SSB4, the overpowered projectile simply ignores the reflector and hits its user anyway. In the case of Ness's and Lucas's forward smashes, should the overpowered projectile collide with the move's hitbox without striking the user, they will undergo a proportionally-substantial amount of lag due to being outprioritized.
Reflectors are generally very useful moves that can be vital, as they help prevent projectile camping and spamming. As such, characters with reliable reflectors tend to have better matchups against characters that rely upon projectiles, such as Samus, than those who lack a reliable reflector.
In addition to the above, Villager is able to grab projectiles and items and store them for later use via Pocket. While not strictly a reflector, retrieved projectiles gain a 1.9x damage multiplier generally associated with reflectors.
List of reflectable attacks