Functional coverage measures the amount of functionality of a design that has been exercised in testing (not the number of functions that have been exercised).
Functional coverage measures the amount of functionality of a design that has been exercised in testing (not the number of functions that have been exercised).
In practice, the term is most frequently used in relation to chip design tools, which is confusing as "functionality" in chip design is very technical, so questions on that topic look a lot like questions on code-coverage.
See also the more general topic of test-coverage.
