Why Cabrillo is a plain-text file layout, developed by Trey Garlough (N5KO) for the ARRL, that contest sponsors use to receive electronic logs. The file starts with a header of tagged lines (callsign, contest name, category, claimed score, operator info) followed by one QSO: line per contact showing frequency, mode, date, time and the exchange sent and received. Most logging programs export it directly, and nearly every major contest sponsor requires logs in this format so their scoring software can read them.
Watch out It is easy to confuse the log file with the on-air activity: Cabrillo is not the exchange you pass during the QSO and it is not a digital transmission mode, it is just how you turn in your log after the contest is over.
Cabrillo = the log you mail in, not the words you say on air.