The topic is Cash vs. Accrual accounting.
Basically, you have to choose one of these accounting methods . . . at least until your company gets large. There are specific thresholds at which you are required operate on an Accrual method.
For small businesses, you still have choices.
Personally, I have always used the Accrual method of accounting my businesses. Here I explain why I do that and how it helps me keep revenue and cost of goods sold lines up in my accounting system.
Feedback welcome, as always.