Wiktionary
business logic
n. (context computing English) Algorithms in a software system that models real life business objects and their interactions.
Wikipedia
Business logic
In computer software, business logic or domain logic is the part of the program that encodes the real-world business rules that determine how data can be created, displayed, stored, and changed. It is contrasted with the remainder of the software that might be concerned with lower-level details of managing a database or displaying the user interface, system infrastructure, or generally connecting various parts of the program.