The document discusses inner product spaces and orthonormal bases. It defines an inner product space as a vector space with an inner product defined on it. An orthonormal basis is introduced as a set of orthogonal unit vectors that form a basis. The Gram-Schmidt process is presented as a method for transforming a basis into an orthonormal basis. Properties of inner products, such as the Cauchy-Schwarz inequality and orthogonal projections, are covered.