In historical terms, an epoch is a moment in time that is chosen as the beginning of a particular era. For example, the beginning of the Gregorian calendar indicates the beginning of the Western Christian era.
The word epoch derives from the Latin epocha, which means "date from which following years are numbered". In turn, this derives from the Ancient Greek, epokhē, which means "fixed point of time".
The pronunciation of epoch changes between British English and American English. In the UK, epoch is pronounced as ee-pok, with a long (or strong) "e". In the US, epoch is pronounced similarly to the word "epic", but not in an identical manner. Epoch in the US is pronounced eh-puhk, with a short (or soft) "e" and with the second part sounding slightly more like the word "puck" than "pick"