Sage

A is someone who is able to utilise, and has mastered the art of Sage Mode or someone given said title because of their renown for their great power, wisdom, or holy standing.

Senjutsu
Very few people are shown to master senjutsu. Naruto Uzumaki, Kabuto Yakushi and Jiraiya are the only three human beings seen using it, with Naruto and Kabuto the only two of the three to perfect it. This is because both learning and using senjutsu is not safe; death may easily occur while learning to use it. Fukasaku claims that the toad sculptures on Mount Myōboku are those who failed to master the art of senjutsu.

Other Uses
"Sage" can also refer to an individual renowned for their great power, wisdom, or holy standing. One of the most famous sages in the series was the Sage of the Six Paths, a legendary figure who discovered chakra, created modern ninjutsu, the one who saved the world from the Ten-Tails and was the first jinchūriki.