What is HTML <script> Tag ?

 HTML <script> tag is used to define a client-side script, such as a JavaScript, j-uery .
It's uses for  image manipulation, form validation, and dynamic changes of content.

Example
<script>
document.write("Hello Friend!")
</script>

we can also use external JavaScrip file on HTML page through this tag

example 

<script type="text/javascript" src="extrnl_avascript.js"></script>