In the Bookings module, bookings can have one of three states: Booked, Pending, and Locked. This is illustrated in the legend displayed in the bottom-right corner of the Bookings window:
This is what the states mean:
Booked - This means the item has been booked by you and has been approved or is confirmed as booked at this time.
Pending - This means moderation is enabled for this resource, and someone else has already flagged this resource at this time, but it has not been approved yet.
Locked - This means the item has been booked by someone else and has been approved, and can only be 'unlocked' or edited by the user who made the booking, Administrators, or those with moderation rights for that category of resources.