1) In general, a mnemonic (from Greek mnemon or mindful; pronounced neh-MAHN-ik ) is a memory aid, such as an abbreviation, rhyme or mental image that helps to remember something. The technique of developing these remembering devices is called "mnemonics." Mnemonics can be used to remember phone numbers, all your new department colleagues' names or the years of the reigns of the Kings and Queens of England. A number of approaches are used.
Here's a mnemonic device for remembering a list of unrelated items in order: Start at the top of the list and make up an outlandish story connecting the first item to the next, continue by connecting the second item to the third, and so on. When your story is done and the list is removed, you'll have a mental picture of a story that, as you recall its progression, will lead you from one remembered item to the next.
2) In computer assembler (or assembly) language, a mnemonic is an abbreviation for an operation. It's entered in the operation code field of each assembler program instruction. For example, on an Intel microprocessor, inc ("increase by one") is a mnemonic. On an IBM System/370 series computer, BAL is a mnemonic for "branch-and-link."