Too out of context to answer for sure.  Is this from Richard's code?

It is likely that those are either fields in a table or variables set up to hold a value.
Boolean is a type of data.  yes/no, true/false, on/off.

See the Microsoft Access Outlines for additional info.  Boolean is covered in multiple places. Expert 8, Yes/No Fields in TechHelp.
Just use Ctrl-F (find) to search for words or phrases on that page.  It is a listing of ALL the courses and what is covered.