There are about 100 species of birds which lay their eggs in the nests of other bird species. The species at the receiving end is called the host species, and the species at the giving end is called the brood parasite.
In human terms, the concept of host is about the same as the concept of foster parents, people who bring up children who are not their own!
The two concepts, host and brood parasite, are so interconnected that they are dealt with together, in the discussion here. But the photograph below is a graphic description of the two concepts!
