A comic strip which is not split across multiple parts but rather is entirely self-contained within a single instalment is commonly described in Sonic the Comic as a Complete Story. It is a term synonymous with oneshot.
The term was not initially widely used in the early days of Sonic the Comic, despite the majority of main strips being one-off stories. One of the earliest appearances of the label was given to Issue 40's Decap Attack strip "The Replacement". The strip was unique in that it was the first "Sega Superstars" strip to not be serial, instead fully contained within four pages. The "Decap Attack" logo was accompanied by a star containing the words "one-off special".
The words "complete story" first appeared in a main story as part of Issue 54's "Beware Predicto!" and continued in the next one-off, "Spinball Wizard", albeit 19 issues later (as all stories in between were multi-parters).
Usage of the term occasionally appears in Sonic the Comic Online, albeit sparingly as the majority of the online continuation's strips are one-offs.