In the interactive go tool pprof session, what is the difference between the 'flat' and 'cum' columns for a function?

(pprof) top flat flat% sum% cum cum% 1.20s 40.0% 40.0% 2.10s 70.0% parseLine 0.50s 16.7% 56.7% 0.50s 16.7% bytes.IndexByte