Homage is the personal declaration of allegiance from a vassal to his/her liege. It is distinct from fealty in many ways, not least of which is that although one can be in fealty to many lords for many fiefs, homage is usually only given to a single lord. Homage also tend to imply more far-reaching duties and requirements on the part of the vassal. To offer homage is to "be the lord's man," while fealty implies no such relationship.
This, however, is a very rough gloss over a very complicated subject and the interested reader is encouraged to seek elsewhere for more thorough discussions.