Different between Tags, Keywords and Key phrase in SEO?

[Venu]

I know keyword is a word that is heart of SEO, but the SEO specialists use it to optimize properly. I am confusing with these three meanings exactly. I seems

Key phrase: Set of 2 or more words. Used in the search field in the google. The keyword Proximity depends on Key phrases.
eg: SEO company in Noida. (4 words)

Keyword: A single word to be optimize, but most of the seo specialists key phrases also called keywords.
eg: SEO company.
my doubt is it's not a single keyword.(2 words).

Tags: The individual words without any meaning.
eg: SEO, Company, Noida, ....

Exactly let me know difference between tags and keywords.

[Jake]

Tags can contain keywords as well, they are used to help categorize and cross-reference site entries. As the excess use of keywords in the text of an articles is considered SEO spam, so is the excess use of tags.

An article on dog training might contain the popular keywords:
Dog training
Obedience
Dog tricks

Tags might include words related to the article but not directly related to dog training, as well as keywords:
Tutorial
Careers
Clicker Training
Electric Collars

[Sneha]

Tags : Tags are self-assigned “labels” that you can use to categorize the posts on your blog.

Keywords : Keywords are used by search engines to identify what your blog and your blog articles are about. A search engine knows what terms are highly searched by users, and looks for those words and phrases on web pages.

Hope you have understood now