From SEO point of view there are 3 meta tags which are too important,
Meta Title - length upto 60-65 characters
Meta Description - upto 150-160 characters
Meta Keywords - upto 160-170 characters
Based on Google SERPs, title tag and meta description character limits have decreased 21% and 23%, respectively.
Now it is 55 characters (including spaces) for title tags and 115 characters (including spaces) for meta descriptions
meta name description
meta name keywords
meta name robots
meta name revisit-after
meta name abstract
meta name author
meta name contact
meta name copyright
meta name distribution
meta name expires
meta name generator
meta name googlebot
meta name language
meta name news keywords
meta name no email
meta name rating
meta name reply-to
meta name slurp
meta name webauthor
meta equiv cache-control
meta equiv content-type
meta equiv cookie
meta equiv disposition
meta equiv imagetoolbar
meta equiv ms theme
meta equiv pics-label
meta equiv pragma
meta equiv refresh
meta equiv resource type
meta equiv script-type
meta equiv style-type
meta equiv window-target
meta data Dublin Core
Meta tag Rel="nofollow"
Meta tag Rel="canonical"
Miscellaneous Meta Tags
Miscellaneous http-equiv
There are 14 Meta tags are:
1. Description Meta Tag
2. Generator Meta Tag
3. Keywords Meta Tag
4. Revisit-After Meta Tag
5. Robots Meta Tag
6. Content-Type Meta Tag
7. No-Cache Meta Tag
8. Audience Meta Tag
9. Author Meta Tag
10. Content-Language Meta Tag
11. Page-Topic Meta Tag
12. Page-Type Meta Tag
13. Prog Id Meta Tag
14. Publisher Meta Tag