Amitabha Buddha
Refers to Amitabha Buddha in Pure Land Buddhism. Often appears in the nembutsu chant 南無阿弥陀仏.
In Jodo Shu, they chant 'Namu Amida Butsu'.
阿弥陀仏 spells out '仏' (Buddha) explicitly and sounds more formal or doctrinal, while 阿弥陀 alone is the common everyday name for the same deity.
From Sanskrit Amitābha, meaning 'infinite light', via Chinese 阿彌陀佛.