A linear operator is a mapping between two vector spaces that preserves the operations of vector addition and scalar multiplication. It is a fundamental concept in linear algebra and functional analysis, often used to describe transformations in mathematical systems and physical phenomena.
Adjoint operators are linear transformations that generalize the concept of the transpose of a matrix to infinite-dimensional spaces, often used in functional analysis. They provide a framework for understanding the duality between different function spaces, playing a crucial role in quantum mechanics and differential equations.