Russellianism: The meanings of our (referential) words are the objects to which they refer. When I say "Socrates is mortal", the meaning of the word `Socrates' in that sentence is a particular person who lived in ancient Greece.

Fregeanism: The meanings of our words are not directly objects in the world but the particular way we conceive of those objects. Two words referring to the same object can have different meaning since they correspond to different ways of conceiving the object. For instance, "morning star" and "evening star" both refer to to the same object (Venus), but they have different meanings.