what are hashtags used for?

[raafa]

I see them a lot now on facebook and instagram, but I don't really understand their function, I also see a lot of pages on jnstagram creating photography competitions and asking participants to use a specific hash tag in order to enter.... Ect... In brief: explain hash tags to me

[Neil Peterson]

Hash tags are used as a statement.

[Walter M]

It's basically a way you can group similar things together. You can think of them as keywords. Twitter just isn't as smart as google so they have to use hashtags, but thats ok.

You can see whats trending and stuff. I never really looked at this stuff before but: http://trendsmap.com/

[EddieJ]

There are no rules for them, so it means whatever the person typing it meant.

It is most often supposed to be a search term, but people often use it just for emphasis.

[Chris]

It's just a way of manually tagging your post with keywords.
The competition people only need to search all instagram posts for the specific hashtag and bam, they have all the entries in one place.