
Brenna S. answered 07/10/19
Thesis Written about Film with Continued Research and Teaching
If you're talking about a character who dies briefly after their introduction, we generally refer to those people as "redshirts." Think of a battle in a movie or TV show--you're much more likely to see the nondescript extras dies before any main or supporting characters die. By having redshirts, we can see the consequences of the battle without losing the characters we care about (immediately, anyway).
If you mean "only there to die" in a more dramatic sense, though, like a character who is martyred, that usually refers to bigger questions of story arcs or character development, and maybe even fate. These issues are more subjective and based on story specifics.