What is cockcrow?

Some articles on cockcrow:

Misa De Gallo
... At midnight "just after the cockcrow", ad praesepium (before the crib), in a small oratory located behind the high altar of the Basilica of Santa Maria Maggiore ... The discrepancy with today's time for the cockcrow is due to the fact that ancient Romans set the cockcrow at the start of the day, i.e ...