To vaporize is to evaporate and turn into gas. If you're watching a sci-fi movie, it probably means to vanish quickly or be utterly obliterated by a phaser gun.
As the structure of the word suggests, vaporize means "turn into vapor." Sometimes this means just turning into gas, like when boiling water turns into steam and rises into the atmosphere. Other times, something more concentrated is left behind, like when maple sap is boiled down into syrup. And in the greenhouse (or grocery store produce section), to vaporize is also to spray your green things with a light coating of mist.