

Assets and liabilities are positions: what stands at a moment. Income sources and expenses are activity: what passed over a period. Each class is read on its own, never netted into one figure.
“Account” means an asset or a liability. An expense is a category and an income item a source; they hold no money, only count what passes through.
A side you leave blank isn’t named: the transaction shows only the side you did name, and keeps the books balanced until you sort it.
See Accounts and classes.