What is billed time?

Billed time is tracked time that has been turned into a charge to a client.

The chain is: you track time against a task, that time is marked billable, and billable time is then gathered into what the client is actually charged. Tracking alone bills nobody — the marking is what decides which hours are chargeable.

This is why locked entries matter. Time records feed invoicing, reporting and pay, so once the record closes it stops being editable.