What is the meaning of Underline?

A line placed underneath a piece of text in order to provide emphasis or to indicate that it should be viewed in italics or (in electronic documents) that it acts as a hyperlink.

The character _.

An announcement of a theatrical performance to follow, placed in an advertisement for the current one.

A caption beneath a photograph (which may have more than one line of text).

To draw a line underneath something, especially to add emphasis.

To emphasise or stress something.

To influence secretly.

Passing under a railway line.

underscore (name of the character _)

Source: wiktionary.org