General Sharepoint What is a Web Part Question

I'm learning SharePoint development. I read some general how to build a web part, but I'm wondering what a web part is in 开发者_StackOverflowgeneral? Big picture, why are they used, what problem is it solving?

Think of a Web Part as a reusable custom web control that is placed, positioned, and whose attributes are set in the browser instead of in Visual Studio. Since SharePoint places such a high priority on customization and content authoring, there needs to be a way for a non-developer to add or modify controls on the web page. Web Parts are that way.