Hash Tag

[Jae1000000]

What does it mean when there is the hash tag symbol before a word or sentence,what does it mean when the hash tag symbol appears after the word or sentence, also what does it mean when the hash tag symbol appear at the beginning and end. For example: #happy,happy#,#happy#. What does all this mean.
Thanks to any one who can explain

[Mamyalynne]

http://contests.about.com/od/g/g/hashtagsdefinition.htm

[Jae1000000]

Mamyalynne: Thanks for the link.