What's the reserve?
As time passes, the necessity arises for repair and/or replacement of items such as the roof, balconies, heating system and the like. Should the condo association wait until these issues actually arise, a large amount of money would have to be collected in a short amount of time from the condo owners, in the form of a "special assessment." Rather than wait until that time, it is typically more sensible for the association to save a bit of money every month from each condo owner's assessment fee and put it toward the reserve, where it can grow and earn interest until such time when it is needed.
More about Association Reserves