some time ago; for a long time now
Often used adverbially with から to mean 'since some time ago' or 'for a while now'. The exact time span is vague and context-dependent.
See also: 前々から
I finally went to the shop I'd been curious about for a while.
I've been hearing about that for some time now.
That had been the plan for a long time already.
前々 points to a vague stretch of time before now, while 後々 points to a vague stretch of time still to come.
Standard kanji spelling; the repetition mark 々 is used for the second 前.
Alternative spelling without the repetition mark; less common but still encountered.
Reduplication of 前 (まえ, 'before') for emphasis, creating a sense of 'some time ago' or 'for a while now'. The exact origin is straightforward and follows a common pattern in Japanese.