P ⊆ NP ⊆ PSPACE ⊆ EXPTIME ⊆ EXPSPACE

P (Polynomial Time)
Decision problems solvable by a deterministic Turing machine in polynomial time.

NP (Nondeterministic Polynomial Time)
Decision problems where a "yes" answer can be verified in polynomial time.

PSPACE (Polynomial Space)
Problems solvable using polynomial space (but possibly exponential time).

EXPTIME (Exponential Time)
Problems solvable in exponential time O(2^p(n)).

EXPSPACE (Exponential Space)
Problems solvable using exponential space O(2^q(n)).

Note: P ⊂ EXPTIME and PSPACE ⊂ EXPSPACE are known strict inclusions,
but whether P = NP remains one of the most famous open problems in computer science.