In biological and evolutionary terms, this is taken to mean a population or species - even an individual or feature - that has become adapted to a very specific niche or task. A good example would be soldier termites; some have jaws so large and specialised for attacking intruders that they can no longer feed themselves. They are kept alive by the worker termites they are defending. Other examples might be the tapeworm, that can only live inside a host's gut or the camouflage of a crab spider to a specific flower - so much so that it cannot hide in any other flower. Specialisation is not always a negative thing, but it can limit the species' ability to adapt further to changing environments.