You can set up abbreviated or short-hand codes in the Auto Complete screen (Settings > Display & Formatting). After you create the codes along with their descriptions there, you can then use them in the memos for time entry, expense entry, etc.

As an example, you can create a shorthand code 'TY'. Then when you enter a memo, say in the Time Entries screen, just enter 'TY' and press Tab. This replaces your abbreviation or shorthand code with the detailed description set up in the Auto Complete screen, say 'Thank you!'. Check CORE Help Center for details and also check out the video on Using Auto Complete.