The document defines several key concepts in abstract algebra including groups, abelian groups, subgroups, isomorphic groups, normal subgroups, quotient groups, and homomorphisms. A group is a set with a binary operation satisfying closure, associativity, identity, and inverse properties. An abelian group additionally requires the binary operation be commutative. A subgroup is a subset of a group that also forms a group. Isomorphic groups have the same structure despite notational differences. Normal subgroups allow the formation of quotient groups by considering left and right cosets. A homomorphism between groups preserves the group operation.