The original Super Saiyan, the first to debut in the long lineage of transformations in the series of Dragon Ball.
On Danbooru, this tag also refers to the sub-forms of SS1, those being Stage 2 (Second Grade, ex. Super Vegeta), Stage 3 (Third Grade, ex. Super Trunks), and Stage 4 (Fourth Grade, Full Power Super Saiyan), as well as the non-canon A- and C-Types that Broly uses (B-Type referring to the Legendary Super Saiyan).