score:6
It's a convoluted way of saying "these fares may not be available during dates that we decide". For example, one of the fares is listed as being valid "6 August 2018 - 31 January 2019", but if you click through to December you'll see that prices double around Christmas. This is because the discounted fares are either no longer available or (more likely) were never available in the first place, hence "embargo".
And no, you can't find the periods anywhere, because Air Asia reserves the right to change them without notice.