Let \(M\) be a module over a commutative ring \(R\), equipped with a quadratic form \(Q: M \to R\).
Let \(\iota : M \to _{l[R]} T(M)\) be the canonical \(R\)-linear map for the tensor algebra \(T(M)\).
Let \(\mathit {1} : R \to _{+*} T(M)\) be the canonical map from \(R\) to \(T(M)\), as a ring homomorphism.
A Clifford algebra over \(Q\), denoted \(\mathcal {C}\kern -2pt\ell (Q)\), is
the ring quotient of the tensor algebra \(T(M)\)
by the equivalence relation satisfying \(\iota (m)^2 \sim \mathit {1}(Q(m))\) for all \(m \in M\).
The natural quotient map is denoted \(\pi : T(M) \to \mathcal {C}\kern -2pt\ell (Q)\) in some literatures,
or \(\pi _\Phi \)/\(\pi _Q\) to emphasize the bilinear form \(\Phi \) or the quadratic form \(Q\), respectively.