standing split
When a character is standing on one leg while the other leg is raised so high that it looks like the person is doing a vertical split.
Not to be confused for a high kick or axe kick.
In October 2020, the pose became a Twitter meme under the hashtag #I字バランス部. It originated with Danbooru post #4129230 and Danbooru post #4119640; see Danbooru comment #2047996 for details.