sapiens

In the social psychological literature, prejudice is considered to be the general attitude you have toward members of a particular group. A prejudice can be positive or negative. Typically, it has an affective component.

Discrimination typically refers to behaviors directed toward others because of their group membership.

Stereotypes (in the social psych literature) refers to generalized beliefs we hold about groups - what we think members of a particular group are like.

Racism, in my opinion, is a combination of some or all of the above related to a particular racial group (such as they are).

Most of the social psych literature I am familiar with makes the distinctions above. That doesn't make the distinctions above any more or less valid than anyone else's opinion, though if you're reading social psych studies about the topic, such definitions might help.