You can set up abbreviated or short-hand codes in the Auto Complete screen (Productivity Tools > Auto Complete). 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!'.
To use the Auto Complete shorthand codes in memos, just type your code and press the Tab key. The code expands into full text that you set in the Auto Complete screen. Check CORE Help Center for details and also check out the video on Using Auto Complete.