What is the purpose of a #hashtag?

[Seasons]

Someone please help me understand the purpose of a #hashtag. I really don't understand it. Is it just to phrase related to your tweet or what?
#helpmeplease

[Mandy]

The purpose of hash tags is to make the tweet more visible to other users, so it's more likely to get retweeted.

[Flaka Silva]

Hash tags ; is just to tag a specific thing and to help you gain followers or get like on your picture such as #like , #lik4follow those are examples .

[Meko]

It is actually from Twitter for trending topics with that website. But some people are using #hashtag in other websites like facebook and instagram.

[Joey]

It is a symbols for number, or if after a number (3#) it means pounds, can also be use in music, and i dont know why people use it how they do now