The AABB thing is the sequence of phrases - usually 8 bars, but sometimes 4 or 12 (and some peculiarities that belong to specific tunes or country dances - e.g. Robin the Og which a 14 bar dance!). A 2-phrase tune may, for example, be AB (16 bars), AAB (24 bars), AABB (32 bars), AABBAB (48 bars)etc. - variable according to the length AND structure of the dance. A 3-phrase dance may, for example, be ABC (24 bars), AABC (32 bars), AABBC or AABCC or ABBCC (40 bars), AABBCC (48 bars) etc. and so on. Then a 64 bar dance mnight be 2x32, or AABBCCDD of a 4-phrase tune (e.g. The Foxhunt - slipjig) etc.

All this is true whether we're taking about Country Dance, Morris (don't forget the once to yourself i.e. one phrase), of just tune sessions!

The art if for the band to know what it's doing, and for the band and caller to negotiate what is within the band's/caller's/dancers' capabilities.

Does that help?

Tom