What does the term rolled off highs mean ?

is there a certain frequency that should be achieved before rolling off ?

No, it is a arbitrary thing...

whatever device it is that is 'rolled off' determines it.

The way i have interpeted the reviewers comments about rolled off highs made me think it was a derogatory term ?

well yes in a way it is because 'perfect' sound on a chart would be a flat line but some may prefer a bit of a roll off so the tweeter is not too bright in a reflective room (for instance).

stereos are far from perfect so a little roll off can be good or can be viewed as bad

there is no absolute

Generally, when someone describes the highs as "rolled off", they feel like the high's are dropping off before 20,000 cycles. Generally, a flat frequency response is desired between 20Hz-20kHz (typical child hearing range). I would guess that many/most of the users here can't really hear much above 15-16 kHz.

Philjolet is correct in calling it arbitrary. Some prefer a perfectly flat frequency response, others prefer rolled of highs to keep your average recording from getting too bright.