Pending User Confirmation - booking confirmation mode is set to "by customer via email" under your Dashboard > Accommodation > Settings > General tab > Booking Confirmation section. Once a booking is placed, the guest will receive an email with a confirmation link, so it needs to be clicked in order to confirm a booking. Before it is done, booking stays with this status.
Pending Payment - booking confirmation mode is set to "confirmation upon payment". In this case, the guest will have to pay for the booking right after it was placed. So until the system confirms that the payment is received, the booking stays with this status.
Pending Admin - booking confirmation mode is set to "by admin manually". So in this case admin have to manually confirm all bookings that may be found under the Dashboard > Bookings > All Bookings. Until it's done, this status is assigned.
Abandoned - booking confirmation mode is set to either "by customer via email" or "confirmation upon payment". There are time limits for the user to confirm a booking via email or by paying for it. In case payment or confirmation is overdue, booking status changes from "pending payment" or "pending user confirmation" to "abandoned".
Confirmed - pretty self-explanatory, booking either confirmed by email, by payment, or manually by admin.
Canceled - booking is canceled by admin from the Dashboard or by guest by email if you include a cancellation link into customers' emails. This option may be found at Accommodation > Settings > General tab > Booking Cancellation section.