Blocks
From MoodleDocs
Blocks are items which may be added to the side inside the block drawer of any page in Moodle. Different themes allow blocks to be added to the left, right or both sides. They may also be added to the centre of the Dashboard.
Any block can be made 'sticky' so that it appears in all the contexts below, such as throughout a course or a particular activity - see Block settings.
If a responsive theme, such as Boost, is used, blocks will be accessible from the bottom of smaller screens, below the main content.
Standard blocks
Available blocks include:
There are also many contributed blocks available for download from the Moodle plugins directory.