“6.18.18” is a tribute to XXXTENTACION. The title references the late XXXTENTACION’s death, in which he was shot and killed on the 18th of June, 2018. This song was originally supposed to be on Eilish’s debut album but didn’t appear on the tracklist.
Eilish performed the song a single time in Oakland, on the first night of her sold-out 1 By 1 Tour, before permanently removing it from the setlist, supposedly due to the controversy surrounding the late rapper.

She described XXXTENTACION in her interview with Complex:

“It’s about a friend of mine that passed recently […] this song is about a very powerful person that no matter what was going on in his life, he was always there for me and he made me feel okay when nothing else did”.

Billie spoke about XXXTENTACION’s death further in an interview with MONTREALITY.