Exactly what does synchronize meas with respect to eM Client?

I am brand new to eM Client and am just trying to learn the terminology.  To what does eM Client synchronize?

Thank you.

eM Client synchronizes emails, contacts, calendars and tasks between eM Client and a server (i.e., google, exchange).  As a result, the data in your eM Client mirrors the server.  This works for accounts configured as IMAP or Exchange.  POP3 accounts, on the other hand, only download new messages from the server and there is no synchronization.

Thank you very much.