Fremen is a slur used to describe Arabs in a derogatory way. A reference to the Dune series of novels. Their nomadic lives in the desert are similar to that of Arabs. In addition, they also speak Arabic.
The word Fremen is a racial slur that has been used historically to degrade and dehumanize arabs. The word is still used by some people for this purpose, and it is seen as offensive and hurtful to arabs. If you are unsure about whether or not it is appropriate to use the word Fremen, it is best to err on the side of caution and avoid using it in any situation.