A more thorough explanation:

Definition: Substitutional is an adjective that describes something that is capable of taking the place of something else.

For example, a substitutional executor is someone who can take the place of the original executor of a will if they are unable to fulfill their duties. Similarly, substitutional issue refers to a child who is adopted to take the place of a biological child.

These examples illustrate how substitutional means being able to replace or substitute for something else. In both cases, there is a need for someone or something to take the place of another, and the substitutional person or thing is capable of fulfilling that role.