A hypocoristic is a pet name or term of endearment. Often generated as

• a contracted form of a given name (such as Tony from Anthony)
• a given name with a diminutive suffix
  • -ito/-ita in Spanish (such as Carmelina from Carmen)
  • -ie or -y in English (such as Vicky from Victoria)
  • double syllablic in various languages (such as John-John)

See Diminutive.

Related: Hypocoristics for Spanish names