What does "biology only" mean on the AQA Spec?

It means that only students studying the separate science course have to study those topics and can be assessed on them. Any topic that is not 'biology only' is in AQA's GCSE Combined Science course too.

Ah, that makes sense.
The only outstanding thing now is the "HT" stuff which is under the "Biology only" . At least at my school, the triple science class are the only one doing the biology only there is not "higher" or "lower" for it. Correct me if I am wrong however.

Your school has just made the choice to not enter students for the foundation tier. However, all science courses at GCSE level are tiered (with a higher and foundation tier). I rarely encounter situations where a student studying the separate science courses has been entered for the foundation tier, but I have seen it happen before, and AQA do have specimen papers for both tiers in the page for their assessment resources.

Thank you so much I have a clear idea of exactly what I need and thanks again for the quick response!

So HT means higher tier, biology only means triple science only?

Asking because I do triple science, and our mock exams do not include any triple science in them.