Heather has it right, except the amounts and she hit the nail on the head when she mentioned water.
Development (spring and summer, colonies or nucs) - strong 'nectar' to mix with pollen for bee grub (for growing larvae), or for wax production - need 5(?) lots of honey for each amount of wax. No need for water or nectar collection, only pollen (and that may be there already).
Stores (autumn feed) - strong syrup as they need to evaporate the water to emulate honey. They are only moving it, so ideally 18% water, but we can't quite manage that, so strongest we can get in practice.
Winter feed - fondant - they want energy for warmth, usually using honey at ~18% water, fondant is close enough and doesn't leak away (or drown the bees!)
Regards, RAB