Tracer is a playable character in Activision Blizzard's video game Overwatch. She was one of the original characters in the roster, I believe (as in, she was available to play upon the game's release); she is considered a "damage" hero or a "DPS".
Tracer, whose real name is Lena Oxton, joined Overwatch as a pilot, and was the youngest person to ever join Overwatch's flight program. She was the first to test-drive (or test-fly, rather) the Slipstream, a jet fighter plane capable of teleporting. Oh her first flight, something went terribly wrong, and the plane was destroyed. Everyone thought she was dead, until she reappeared one day out of thin air. They figured out that her molecules were desynchronized from the flow of time. (It was like that one episode of Deep Space Nine in which Sisko was trapped in a subspace rift and kept disappearing out of the timeline and coming back like ten years later, not having aged at all. Literally the exact same thing. Tracer kept disappearing from the flow of time and reappearing some time later). Winston (the talking gorilla scientist) worked relentlessly to bring Tracer back, and invented the Chronal Accelerator, which allowed Tracer to control where she was at in time.
Her primary fire are her pulse pistols, extremely rapid-fire pistol weapons that let out a wide spread of medium-damage shots. You hold down the button until your clip is empty, the bullets just spray out.
Her primary and most important ability is "blink", which is just what it sounds like, it allows you to instantly blink (teleport) 7 meters in whatever direction you are moving. She can have a maximum of 3 blinks at a time, and a blink takes 3 seconds to recharge.
Her secondary (but still important) ability is "recall", which blinks her to wherever on the map she was 3 seconds ago, and resets her HP to what it was at that time. This is useful for delving into the thick of it, dealing some quick damage, and then hopping out as soon as you're about to die. It's probably what makes Tracer playable for me, considering she has 150 HP (the lowest number of hitpoints in the game)
The "pulse bomb" is her ultimate ability; it is a little sticky bomb that you throw forward, it travels like a meter-ish and sticks to whoever it hits. It explodes after a second, and deals a large amount of damage. It will, however, stick to shield barriers, and fall off of characters if they teleport (like Moira or Reaper). It's very difficult to land, and doesn't kill tanks at full-ish HP. It also does damage Tracer, so you need to blink out once you throw it or else you will die.