What are the differences between story mode and gta online?

The only verified information available is that Grand Theft Auto: San Andreas is an action‑adventure game featuring a story mode in which the player follows Carl "CJ" Johnson as he returns to his hometown, rebuilds his gang, and investigates his mother’s murder. The source does not mention GTA Online, its features, or how it compares to the story mode. Without evidence that addresses GTA Online, no reliable differences can be cited.