On Moodle, the course material is either a resource or an activity. A resource is an item that the student views, listens to, reads, or downloads. Examples would be:
A web page
A link to another location on the Web
A file that the student downloads
A video that the student watches
An activity is an item that the student interacts with, or one that enables the student to interact with the teacher or other students. Examples would be:
A quiz
An assignment that the student uploads for the teacher to review
A wiki
A forum
Usually, resources are ungraded while activities are graded.