Death

Death is the end of all biological functions in a living organism. It can come about naturally, such as old age or disease, or artificially, such as murder or suicide.

Following death, a person's body is put somewhere to honor their memory like a cemetery.

Most religions have a concept of an eternal life after death, such as the Judaism and Christian concept of Heaven.

Apocalypse named one of his Horsemen Death. The first was Angel, though he used the name Archangel. The second was a mutant who's real name is unknown.

Background
Due to censorship issues, death and all related words, like kill or murder, were not specifically said. Most series implied such things but the words were rarely said.

There is a cosmic entity in the comics who is the personification of Death. For SS undefined, she was renamed Lady Chaos though it is possible Thanos simply got her name wrong and she is Death.