A booking is a single order placed for an event - by a customer online, or by you. Each booking has a status that tells you where its payment stands.
Paid: payment completed.
Unpaid: awaiting payment (e.g. a payment link was sent).
Free: a no-cost booking. A booking discounted to $0 is marked Free too, and the confirmation email sends as normal.
Refunded / Partially refunded: money returned in full or in part.
Cancelled: the booking was cancelled. A cancelled booking keeps its payment status, so you might see Cancelled alongside Refunded.
A red Pending refund flag can appear next to a status when a refund is still owed - for example after cancelling an event - and clears once the refund is processed.
Booking statuses show in-line on your bookings list:

