bird's nest

Short definition from Wiktionary

Noun

1. 1
   A structure built by a bird as a place to incubate its eggs and rear its young.
2. 2
   Any of several plants having some resemblance to the typical nest of a bird, eg., the wild carrot (Daucus carota).
3. 3
   Any tangle of fibers resembling a typical nest of a bird.