noun
long ago; far in the past
Emphasizes a distant, often indefinite time in the past. Used in narrative or reflective contexts.
遥か昔、この地には大きな湖があった。
Long ago, there was a large lake in this area.
それは遥か昔の出来事だ。
That is an event from the distant past.
昔 simply means 'old times' or 'once upon a time', while 遥か昔 stresses a very distant past.
大昔 also means 'ancient times', but 遥か昔 can be more poetic and less specific about the era.
Compound of 遥か (far, distant) and 昔 (old times, past).