What is Development class

Hi experts,

What is development class? I need to transport this to Prod and there are two of them one Dev Class for backend objects and Dev Class for front end objects. I could not find any thread on this and on sap library all I got is, which is not clear to me:

"A group of logically related development objects.

A development class contains all the development objects that must be developed, maintained, and transported together. Typically, the objects that make up a transaction belong to one development class. Customer development classes begin with Y or Z."