The term «Buddhas of the Three Times» refers to the Finders of Truth, Tathagatas (sanskr. tathаgata, tib. de shin sheg pa), who came to the Earth in the past and will be coming here in the future.
In Buddhist symbolism and iconography they are represented by Tathagatas:
Buddha Dipankara (tib. mar me mdzad)
— Tathagata of the Past;
Buddha Shakyamuni (tib. ston-pa shkya-thuba)
— Tathagata the Present;
Buddha Maitreya (tib. byams pa)
— Tathagata of the Future.
The word «Buddha» is not a name, but a concept of something different from all the living beings.
In Sanskrit «Buddha» means «Awakened one» and is defined as a being that fully developed its original nature. In Tibetan the word «buddha» (tib. sangs-rgyas) consists of two parts truly characterizing the very definition of it: a being that «purified oneself» (tib. sangs) from obscuration of ignorance and «spread» (tib. rgyas) its boundless power and compassion.