Booking is pretty similar to Billings but there is a slight difference between them. Considering that your Sales Rep has closed a deal in the amount of $12.000 in January, with monthly payments of $1.000, and we are in April so the amount billed is $1.000 but the bookings are in the amount of $12.000.

If you want to have a more deepened approach to the subject, this article explains the difference between bookings, billings and revenue.