“Racialism” is a word that is used differently by different people. There are many people who simply use it as a synonym for racism. However, it also has a different meaning.
Racism, of course, is the idea that different races are better or worse than other races. It can take the form of thinking that your race is superior to other races. It can also take the form of saying that some other race is worse than others even if you do not say that yours is superior. An example of racism, then, would be if you believe that Africans as a race are lazier and more prone to criminal activity than white people are.
Racialism can be a different idea. It can refer to the idea that different races have different attributes that can be identified objectively but that these differences do not mean that one is superior to the other. To draw an analogy, parents know that their children have different attributes and yet they do not prefer one to the other. Racialism, in theory, can be similar to this. It can hold that different races are different but that no race is better than another race. An example of racialism, then, would be if you believe that black people are inherently more musical than people of other races.
Again, not all people use “racialism” in this way. However, this is what “racialism” means when it is used in a way other than as a synonym for racism.