Homology refers to two things that have an equivalent role or relationship. Homology is important in comparative biology since it makes it possible to determine if two different animals or plants share a common ancestor. Essentially, homology in this context means that there are two species that have related parts that do similar things, but that are not exactly the same.
Following are some examples of homology:
Homologous structures can be traced back to the last common ancestor that the animal's shared. For example, if the wing of a bat and the forearm of a person are examples of homology, this means that the anatomical structure of the forearm and of the wing were both present in the last common ancestor along the evolutionary chain that was shared by the bird and bat.
Now you have lots of examples of homology and you have a better understanding of how homology works in the field of comparative biology.