fractionation

Short definition from Wiktionary

Noun

1. 1
   A separation process in which a certain quantity of a mixture is divided up into smaller quantities (fractions) in which the composition changes according to a gradient; an instance of this process.
2. 2
   The division of a total dose of radiation into fractions.
3. 3
   A preliminary stage of encryption that divides each plaintext symbol into several ciphertext symbols.
4. 4
   A form of hypnosis where the patient is made to enter and leave a trance state many times in quick succession.