Activities
An activity is a general name for a group of features in a Moodle course. Usually an activity is something that a student will do that interacts with other students and or the teacher.
The teacher can add an activity, when editing is turned on by using the "Add an activity" in a course (see Getting started for teachers or Adding resources and activitiesfor more help). There are other ways to add an activity.
In Moodle 2.0 there are 13 different types of activities in the standard Moodle that can be found on the "add an activity" pull down menu.
There are also other interactive modules features, such as Blogs. A a site may add other activities which have been developed as contributed code and found in Moodle.org's Modules and Plugins database for adding to a site.
See also
Activities block - lists all the activities in a course
Activity By 'ID Number'- a standard advance setting used in activities
Activity modules administration - for administrators