noun

• 1A region where the characteristics of one adjacent section or division give way to those of another, sometimes exhibiting features of both.

• 2Specifically. Botany. The region in a plant axis where the structures of the root meet those of the shoot or stem.

• 3Astronomy
  The thin layer of the sun's atmosphere between the chromosphere and the corona, produced by heat flowing from the latter into the former.

• 4The region between the passband and stopband in the frequency response of a filter.

• 5Electronics
  In a semiconductor device: the junction between an N-type and P-type semiconductor.