The most common meaning is simple: something has no “fuel,” so it can’t perform. That might be a car that won’t start, a project that keeps stalling, or a person whose effort or confidence isn’t showing up.
In everyday conversation, the phrase often points to a lack of drive or ability. If someone says, “That plan ain’t got no gas in it,” they’re suggesting it won’t get traction, not that it’s technically wrong.
It can also carry a blunt emotional edge. The speaker might be disappointed, frustrated, or unimpressed—especially if they expected more.