<mark> tag in Html is for highlighting (marked) the text part. If you need to point up that parts of your text, you can use <mark> tag. This is a newly added tag and introduced in HTML5. The text have yellow color background in maximum browsers, if mark tag is applied on it. It can be replaced with different color using CSS background- color property.
<!DOCTYPE html> <html> <head> <title>Mark Tag</title> </head> <body> <h2>Exmaple of Mark Tag</h2> <p>You can easily learn Web designing using <mark>Codingtag Website</mark></p> </body> </html>