For what the target tag is used?

Answer 1

target is a atributte. He specify the target of the link. Example:
<a href="http://www.google.com" target="_blank">Google </a>
Open a home Google in a new window or tab.

Answer 2

First of all target is not a tag. It is an attribute.
Target attribute specifies where to open the linked document. Target attribute can have one of the following values.
_blank - Opens the linked document in a new window or tab
_self - Opens the linked document in the same window/tab as it was clicked (this is default)
_parent - Opens the linked document in the parent frame
_top - Opens the linked document in the full body of the window
framename - Opens the linked document in a named frame.

Answer 3

Target attribute defines how your linked document will be opened. Target attribute can have one of the following values.
_blank - Opens the linked document in a new window or tab
_self - Opens the linked document in the same frame as it was clicked (this is default)
_parent - Opens the linked document in the parent frame
_top - Opens the linked document in the full body of the window