The iconic costume worn by the Sailor Senshi in Bishoujo Senshi Sailor Moon. Its basic design is comprised of the following, starting from the top:
Each of the Sailor Senshi wear different theme colors and have design variations of the above, but the overall uniform is generally the same.
Due to them wearing skirts, it's not immediately obvious that they are wearing leotards. Because of this, images where the leotard can be seen from under the skirt usually get tagged as white panties due to Danbooru's policy of "tag what you see".
Note that this uniform represents Earth's Sailor Senshi, while warriors from different star systems like the Sailor Starlights and Shadow Galactica have completely different designs, with the sailor collar being the only consistent design aspect.