HTML <Blockquote> tag is used when there is quote in the statement from source other than the website which is provided in the referral lines.

About HTML
Here is a quote from Wiki on HTML:


HyperText Markup Language (HTML) is the standard markup language for creating web pages and web applications. With Cascading Style Sheets (CSS), and JavaScript, it forms a triad of cornerstone technologies for the World Wide Web.


Source here 

Cite attribute is attached with it for referring to the source of the statement or quote. It also supports all global HTML attributes along with event attributes too. There is default CSS attached with this HTML tag which can be altered by simply replacing the new values in the stylesheet.