His name as an retired emperor came from 'Reizei in,' which was built by Emperor Saga on the northeast of the current Nijo-jo Castle as his detached palace; it was an imperial villa that later became Go-in (retired emperor's palace).
上皇になった際の名称は、現在の二条城の東北に嵯峨天皇が造営した離宮「冷然院」が後に後院（上皇の御所）となった「冷泉院」に由来する。