This means the flight looks fairly empty at the moment. P and A are First Class fare buckets, J, C, I, O are Business, and everything else is Economy (Y is the highest fare, then working left to right the fares are cheaper). The number indicates that there are at least that number of seats available in that fare bucket.

So, overall there are at least 8 empty seats in F, 28 in J, and at least 100 empty in Y.