Two structures in biology are said to be analogous if they perform a similar function by a simlar mechanism, but did not arise from a common ancestor performing that function: for example, the wings of insects and the wings of birds. These similar structures most likely evolved through different pathways, a process known as convergent evolution.
The concept of analogy is contrasted with that of homology, which refers to two structures that share a common ancestor. The may retain the function of the common ancestor, or they may have evolved to fulfil quite distinct functions.