This trope applies when an LGBT character is killed off, and is especially harmful when it happens shortly after or alongside a positive development with regards to their orientation, further linking the character’s orientation to the death of the character.
Historically, LGBT characters have not been allowed happy endings. Once mandated by the broadcasting standards Hayes Code, “deviant” characters (including all LGBT characters) must not be made sympathetic or rewarded, and narrative punishment for this behavior remains pervasive even now that mainstream attitudes and laws have changed. The key problem isn’t merely that LGBT characters are killed off, but the tendency that these characters, and in particular lesbian and bisexual female characters, are killed off far more often than straight characters.
Given the low overall numbers of LGBT characters in the media and the important representation those characters provide to viewers, the loss of any one of those characters is more keenly felt. The trope was revived in 2015/16 and it seems to continue in the 2016/17 season – particularly for female lesbian or bisexual characters (the trope is commonly known as the Lesbian Death Trope).