i've seen it used to describe both nazism(national socialism)and communism but i don't know which one is the true one
if it's communism,how can we call nazism to avoid the word?

National Socialism is the complete opposite of communism in every way. When someone just says "Socialism," and they do not say "National Socialism," then they are usually talking about communism.

The Socialism in National Socialism is only in its opposition to Capitalism, which is as unSatanic as Communism/Marxism.

Nazism or national Socialism is influenced by prussian socialism, a kind of socialism completely distinct from marxist socialism and infact in complete opposition to it. You might want to read Oswald spenglers books I.e if you get correct translations.