Lindsay Lohan and Samantha Ronson are NOT getting back together ... sources close to Lindsay tell TMZ -- despite reports the two were all over each other this week at a NYC nightclub.

Lindsay did hang out with Sam Thursday night at Le Baron in New York -- but sources tell TMZ, there was no touchy-feely business going on ... it was just two old friends catching up together.

There were reports the two might have rekindled a relationship -- but we're told that's not true ... neither Lindsay nor Sam has plans to reunite romantically.

We're told the two are simply focusing on mending their friendship after a rough break-up in 2009. They began dating on-and-off in 2007.

As one source put it -- they're "just friends. That's it. Nothing more."