Prefatory
/ˈprefətɔːri/
Definition 1 of 1
Pro Tip 1/3Introductory Nature
Prefatory means something is beginning or opening, often setting the stage for what follows. 
The book's prefatory section gives a brief history of the subject.
Pro Tip 2/3Academic Usage
Prefatory is commonly used in academic texts to describe introductory material. 
Her thesis includes a prefatory chapter that outlines the methodology.
Pro Tip 3/3Not Always Necessary
While prefatory elements can be helpful, they are not required in all contexts. 
Despite not having a prefatory explanation, the film begins abruptly.