The meta description tag is a short description of the current page that is used by certain search engines as a quick page summary on their result pages. It is typically a good idea to keep this description shorter than 255 characters as most search engines place restriction on the length allowed for this field.
ex: A great article on the importance of using the meta description tag

A comma-separated list of keywords and keyword phrases that are pertinent to the current page. This list is used by certain search engines to categorize or rank your page. Like the meta description tag, some search engines place restrictions on this field so it is typically a good idea to keep it under 255 characters.
ex: Search Engine Optimization, Meta Tags, Meta Description, Meta Keywords

The full name of the author of the current page.
ex: John Smith

An unofficial copyright for the information on the current page. You should note that this copyright is usually not considered legally binding.
ex: Copyright 1996-2006 CoffeeCup Software, All Rights Reserved

A flag that certain search engines will use to determine how the current page will be indexed.
All — The current page will be indexed and all links will be followed
index, nofollow — The current page will be indexed but none of the links will be followed
noindex, follow — The current page will not be indexed but the links will still be followed
noindex, nofollow — The current page will not be indexed and none of the links will be followed

The number of days that certain search engines will wait before spidering your page for new content.
ex: 31 days

This rating is used by certain search engines and user-agents for content filtering.
Safe for kids — For content that is safe for everyone.
General — Young children should have parental guidance.
14 Years — Not Safe for children under 14.
Mature — Not safe for children under 17
Restricted — View at your own risk