recombination

Short definition from Wiktionary

Noun

1. 1
   Combination a second or subsequent time.
2. 2
   The formation of genetic combinations in offspring that are not present in the parents.
3. 3
   The reverse of dissociation.
4. 4
   The process by which the plasma of electrons and protons produced after the Big Bang condensed into hydrogen, or the epoch in which this process occurred.

Proper noun

1. 1
   The epoch of recombination of the Universe, where atomic matter formed from free particles, combining protons with electrons. One of the Ages of the Universe. The cosmic era when neutral hydrogen formed out of the cosmic soup of protons and electrons in plasma, that condensed out of the energy of the Big Bang. This era produces the Cosmic Microwave Background (CMB).