Pre-slash

The piece of work was a short pre-slash story around Hulkling and Wiccan from The Young Avengers, it was posted under the alias Confidenceiskey on 18 October, 2007.

Source: wiktionary

The first, a lengthy Kirk/Spock pre-slash story “The Immovable Object,” appeared in the zine The Other Side of Paradise, no. 2.

Source: wiktionary

Some pre-slash fan fiction does not develop into slash at all; other stories make it clear that slash may be a possible development in the future but they do not elaborate on it; yet other stories, or better series of stories, include pre-slash chapters or pre-slash stories (which function as one-shot stories and work on their own), but the following stories in the series are already slash.

Source: wiktionary