The difference is huge! I'm assuming you're referring to the Liberal/Democrat/Socialist VS pure Libertarian. Unfortunately, the liberal moniker got to be synonymous with Democrats. That's really too bad. You can easily be liberal and not be a Democrat. Democrat and Socialist should be synonymous. Virtually no difference.
A pure Libertarian wants as little Federal Government interference as possible. So obviously, they are far removed from the Democrat ideology. A liberal also wants little government interference. The reason liberals get lumped in with Democrats is because many vociferous, liberal minded individuals are also Democrat. I think liberal Republicans are automatically Libertarians. Guess I'd fit in with that crowd. And I mean CROWD. I think it's what many refer to as "moderate".
I believe that quite a few liberals in the Democrat camp are misguided. They're against Socialist schemes, but stay in the Democrat camp because of the conservative slant in the GOP corner. By being against socialist programs, they're already leaning toward the center/moderate position. They ought to be Libertarian instead of Democrat. Consequently, their votes are being wasted on the Democrat's slate when you examine the major issues that they don't agree on. It's mind numbingly, irritating when you give it any thought at all!