That which is
corresponding in
structure or
origin, as in part of one
animal to a similar part in another
animal: The
foreleg of a
horse and the
wing of a
bird are
homologs
In genetics it has the specific meaning of sequence identity(origin) and conservation of function(structure). Unfortunately, different people may divide up the genes slightly differently, so it can cause arguments.
This is especially problematic in the rare occasions where convergent evolution occurs. Since the structure is the same, but the origin is not it could be argued that they are analogs instead.