Slashtags are a community-created convention to mark additional metadata of a tweet. They are like hashtags but typically target or indicate other people as the subject of a short word.

Slashtags were named by Chris Blow and introduced by Chris Messina.

Etymology

Unlike hashtags, slashtags aren't precisely named. Or rather, Chris Blow's intention in calling them "slashtags" was to extend the basic hashtag functionality with subtags. That use case is not covered here.

Instead, these words were originally called "pointers", set off with a slash character ("/" — called "the slasher").

Slashtags, therefore, are actually the collection of phrases that appear after the slasher. 

Using slashtags

Also unlike hashtags, each word or phrase in a slashtag stanza does not need its own slash. Instead, ONE slash is used to demarcate the beginning of metadata and various slashtags are used individually or serially:

This is a sample tweet. /via @person1

This is a sample tweet. /via @person1 by @person2 cc @person3

This is a sample tweet. /via @person1 by @person2 cc @person3 @person4

This is incorrect (largely because it adds characters without increasing the amount of meaning):

This is a sample tweet. /via @person1 /by @person2 /cc @person3

You can leave off the slasher, but that decreases the separation between the "meta and the meat":

This is a sample tweet. via @person1 by @person2 cc @person3

List of current slashtags

• by
• cc, for and tip
• thx
• hat tip, ht and via