Google it

https://www.co-optrade.com/forum/crowdfunding-or-reg-a/fundamentals-of-crowdfunding

The simplest way I can help you understand Crowdfunding is by dissecting it into two words CROWD and FUNDING. Crowd can be individual or group of people that are willing to invest in the company or in an idea. Funding is a sum of money set aside to be use for a specific reason. Combining the two words means that a group of people or individuals believing in an idea that are willing to a lot some money to bring that idea to life. the most common example is a Kickstarter.

In general, there are a more detailed description that you can find in the web that will clarify this idea to you.

I would recommend the following sites for reading:

https://hbr.org/2016/04/the-unique-value-of-crowdfunding-is-not-money-its-community

https://www.thebalance.com/a-guide-what-is-crowdfunding-985100

http://www.investopedia.com/terms/c/crowdfunding.asp

https://www.entrepreneur.com/article/228125

*This definition is basic and does not define the whole idea or characteristics that would qualify to be a crowdfunder.