This is the name given to the method of loading parent entities at the same time a querying child entities.

Use .Include(x => x.{property referencing parent entity}) within a linq to DataSets query to load parent entities.

For example

var customers = _context.Customers.Include(x => x.MembershipType);

MembershipType is a parent of Customer. i.e. a MembershipType can have many Customer entities.