Revenue is what you report for tax purposes based on the local applicable accounting rules.
Bookings is also often reported to Wall Street quarterly for software companies and is a great leading indicator of their financial health. For our example above, this would be $500k reported in the month in which the deal was signed.
Sales Credit is whatever you use to measure your sales people. While it is most often tied closely to bookings, it is also common to credit the sales people only when revenue is recognized, or to provide credit based on the margin generated. You could also split credit among members of the selling team. This piece is totally up to you and is part of your comp plan design.
Donya Rose, CSCP, is Managing Principal of The Cygnal Group. She is a recognized expert in sales compensation plan design, regularly speaking at conferences and writing published articles. She serves clients from F500 to growth-stage businesses, and advises WorldatWork on sales compensation hot topics and best practices.