Hashtag: a #hashtag is a way to bring together
disparate users on the same topic, without the
tweets needing to know each other already.
Hashtags can also be a way to archive conversations
on a theme, and discuss events or conferences.
You can click on any #hashtag (for example
#altmetrics) and find all recent tweets which have
included it. This is the best way to tweet around a
specific module (or academic topic).
Direct Message: a DM is a private message, within
the network, which only you and the recipient see.