Magic Missile is an iconic 1st level offensive Wizard spell from Dungeons & Dragons, and is literally one of the oldest attack spells in the entire history of the game. It creates one or more "bullets" of magical energy which are then launched at one - or sometimes multiple - targets. In earlier editions, it's functionally a homing attack which hits automatically, with each bullet doing a relatively small amount of damage, but with each bullet doing its own damage roll, the damage can stack up, making it useful for a surprisingly decent interval.
Since it is so low level and always hits, it pairs nicely with Metamagic to add rider effects. As it's a force effect, almost nothing in the game even resists it (epic Challenge Rating Force Dragons are the only OGL monster to do so), ensuring its low damage will almost always hit.
The spell is so iconic (and it's name so generic) that many gamers will use the name as a catch-all for any low-level "fire energy at somebody" type spells. In Warhammer Fantasy, it's even a distinctive category of attack spells. Despite its iconicity, there is almost no official art of it in official Dungeons & Dragons material. Luckily there's a LOT of art from other franchises, vidyas, and various internet drawfags, if you're looking for something cool to suit your tastes.