What is semantic html?

Question

Someone told me its about blod <b></b> , <strong></strong> , italic<i></i> , <em></em>. If these tags do same work then why we need two.

Answer 1

They have the same effect on normal web browser rendering engines, but there is a fundamental difference between them.
for more info
https://stackoverflow.com/questions/271743/whats-the-difference-between-b-and-strong-i-and-em

Answer 2

A semantic element clearly describes its meaning to both the browser and the developer.
Examples of non-semantic elements: <div> and <span> >>> Tells nothing about its content.
Examples of semantic elements: <form>, <table>, and <article> >>> Clearly defines its content.