What are the peak and low seasons for air travel?

From the UK to Australia.

I don't think there is such a thing as a peak or low season when it comes to air travel! There may be for other things like hotels and such, but air travel I don't think so. If you are looking for a good deal you should look at booking way ahead or try flying standby. Check out all of the airlines and do some comparison shopping.

summer and winter

It really depends on where you want to go. When it is peak in some locations then it is off season in others. There is no set dates. Winter is peak season for ski areas but would be off season for the summer.