asap — usually written ASAP — means as soon as possible. You use it when you want something done quickly: send it ASAP, I need that ASAP. It started in the 1950s. The first known use in a book is from a US officer writing about the Korean War; in the military it first meant something closer to “as soon as we can manage it as a military job.” Now anyone uses it in messages, emails, and spoken work talk. It feels informal and a little pushy, like tapping the table. In a careful letter, write the full words. People say the four letters (A-S-A-P) or run it together like “ay-sap.”