Title Tag

The TITLE tag contains the single most important piece of information within any web document. Title tags are one of the simplest and most successful ways of letting a search understand the focus of the page and allow it to determine the maximum relevancy for it.
The title tag for a web document is placed within the head...head tags for the document using title...title. This textual component of the web document is the first piece of text that a Search Engine will find within a web document and will use it to determine which words and/or phrases the document should be considered as being relevant for. For example if a page has the title tag of "Search Engine Optimization" the page is seen as being focussed for that term.
The title tag also serves a secondary feature which is that it will be displayed by a search engine for a particular query as the Link to that result. This means that users of a search engine will read the tag and use it to ascertain the focus of the returned results and are likely to use this to determine whether or not that particular returned result is relevant to that particular search query. It is for the reason that an optimal title tag should have no more than 64 characters as this is the maximum that Google will display in the search engine results.