The term "Adjoint" appears in many different mathematical areas and for sometimes seemingly different kinds of things. Wikipedia says -- "In mathematics, the term adjoint applies in several situations. Several of these share a similar formalism: if $A$ is adjoint to $B$, then there is typically some formula of the type" $$\left( A x, y \right) = \left(x, B y\right)$$ Also, Wikipedia goes on to give examples and a few of them I repeat here:

• Hermitian Adjoint of a Linear Operator
• Adjoint Equation (as used in Differential Operators)