Britney Spears' Dance Form Attacked by Abby Lee Miller

Britney Spears is now the target of one of the harshest dance critics in the world ... Abby Lee Miller.

As you know, Britney posts lots of Instagram videos of herself dancing, but a clip she put up Thursday crossed the line ... at least it did for Abby, who couldn't hold her tongue, and commented, "Close your rib cage!"

The real shocker here? Plenty of people seemed to agree with Abby ... but yeah, lots more are defending Brit and coming for ALM.

For what it's worth, a closed rib cage is said to help dancers with movement, making transitions more fluid and with less effort.

While her approach in critiquing Britney might've been off ... it's hard to argue with Abby Lee's success when it comes to producing dance talent. Miller was certified by Dance Masters of America in the '80s and opened her own studio which later became "Dance Moms" ... which, of course, gave us JoJo Siwa and Maddie Ziegler.