Bridge

A bridge is a piece of back-end software that "bridges" two protocols, such as Matrix and Telegram, to work with one another and have a good user experience. It is often times used for community group chats to have a "main" open and a backup option for people who prefer. Bridges make the community more inclusive for people who prefer other services.

Though it is important to note that bridges are not Matrix-specific. you can bridge any two protocols. Discord and Telegram, Matrix and Revolt, even Discord and E-Mail. It's an abstract concept which can be implemented by many protocols.

A popular Matrix bridge creator is Tulir Asokan.

Internally, a bridge often uses the Application Service API on the Matrix side, which allows it to register users which can map to a user on another protocol(for example, a Discord bridge running on example.com may have users like @_discord_[ID]:example.com), though that is not always the case.