Different meanings, different sources. Pure mind means to get rid of all distractions, no matter good or bad, and concentrate on doing something Zen, such as the practice of pure mind; Meditation refers to calmly treating everything, such as meditation and rest, without causing emotional fluctuations.
Meditation comes from Zhuangzi Sheng Da: "I will be fascinated, and I will be calm if I dare not consume gas." ; The pure heart comes from "Into qixia temple Mountain": the pure heart holds the ice and snow, and the twilight teeth force Sang Yu.