H1 Tag is high size. Mostly used in Heading
H2 Tag also high size but compel with H1 its a little bit smaller . mostly used in sub heading.
H-3 Tag is almost a little bit high size than normal text used in bold content its acts as alternative of bold font.
h4 is almost near normal text.
H5 is small size text rarely used
H6 is very small . . very rarely used in the text.
There are six heading tags in html <h1>,<h2>,<h3>,<h4>,<h5> and <h6>.
<h1> defines the most important heading. <h6> defines the least important heading.
HTML has six heading tags h1, h2, h3, h4, h5 and h6 with decreasing importance from h1 being most important to h6 being the least important heading tag.