Noun
B story (plural B stories)
Alternative form of B-story
B-story (plural B-stories)
(authorship) A subplot that appears in a screenplay or script for a movie or television show; a subplot that concerns the side-characters or less important aspects of a television show.
B-story
While he was billed as a supporting actor in the 1978 Battlestar Galactica pilot, a majority of his scenes were cut mainly because those scenes dealt with Serina's ( Jane Seymour ) "space cancer " B-story which had been excised from the final cut. Source: Internet