The <base> tag indicates base url/target for all the link in the document.
The <base> tag must be written inside the <head> tag.
This attribute is used to give the base url to the whole document.
In the below example target attribute value is not given for <a> tag, but instead it is given in <base> tag, so every link in the web page will have the target attribute value which is given in the <base> tag.
If the target attribute is given in the <a> tag, then is target attribute value will be taken.