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.
There are 14 different types of activities in the standard Moodle that can be found when the editing is turned on and the link 'Add an activity or resource' is clicked.
Assignments
Enable teachers to grade and give comments on uploaded files and assignments created on and off line
Chat
Allows participants to have a real-time synchronous discussion
Choice
A teacher asks a question and specifies a choice of multiple responses
Database
Enables participants to create, maintain and search a bank of record entries
External tool
Allows participants to interact with LTI compliant learning resources and activities on other web sites.
Feedback
For creating and conducting surveys to collect feedback
Forum
Allows participants to have asynchronous discussions
Glossary
Enables participants to create and maintain a list of definitions, like a dictionary
Lesson
For delivering content in flexible ways
Quiz
Allows the teacher to design and set quiz tests, which may be automatically marked and feedback and/or to correct answers shown
SCORM
Enables SCORM packages to be included as course content
Survey
For gathering data from students to help teachers learn about their class and reflect on their own teaching
Wiki
A collection of web pages that anyone can add to or edit
Workshop
Enables peer assessment