An optical illusion in which lines are drawn in front of and behind a subject, making the subject appear to pop out of the screen.
It became a Twitter meme in December 2019, where it's variously known as 例の線 (rei no sen, lit. "those lines") or 白い線 (shiroi sen, lit. "white lines").
The following tags are aliased to this tag: 3d_lines and rei_no_sen (learn more).