what is meaning of <a href=/>? in html?

/ is the root directory as determined by the web server program.

Proper syntax is:

<a href="http://google.com">Google</a>

<script src="myscript.js"></script>

The first will display as "Google" and send the user to google.com when clicked (a hyperlink).
The second includes a script, with src stating the file name.

<a href=/>
a ->hyperlink
href ->link's destination