Difference between a few tags

Question

What is the difference between :
1.)Bold and Strong tag
2.)Insert and Underline tag
3.)Delete and Strike tag
(Apparently they are doing the same things,so what is the point of introducing new tags?)

Answer 1

The strong doesn't always mean bold text. It's only used to say something is important in your web page. Some browser could display strong tag as normal text...
It might be useful for search engines