Redskin is a slur used to describe Native americans in a derogatory way. The term Redskin, came from two places, the skin color, then the cruel torture of skinning Native Americans for a bounty. Since their skin was red they started saying "red skins."
The word Redskin is a racial slur that has been used historically to degrade and dehumanize native americans. The word is still used by some people for this purpose, and it is seen as offensive and hurtful to native americans. If you are unsure about whether or not it is appropriate to use the word Redskin, it is best to err on the side of caution and avoid using it in any situation.