It's an approach in economics that usually rejects Marx's revolutionary politics but agrees with his critiques of capitalism. People like Richard Wolff identity as Marxian.
Yeah it's not required but the only self identified "Marxians" I've come across were raging liberals while I have met "Marxist" academics that were not liberal.
Libs gonna lib, and sometimes they need to engage with Marx. "Marxian" lets them do that without inviting the red scare bullshit that Marxists will always face.
I've never met anyone who calls themselves "Marxian." Only seen it used to describe Marxist economic theory without discussion of Marxist political prescriptions or history.