what is the meaning of RenderPartial?

It is an extension method of the HtmlHelper class.
The RenderPartial method renders an ASP.NET user control (.ascx/.cshtml file) as a partial view.
You will find below links useful:
https://msdn.microsoft.com/en-us/library/system.web.mvc.html.renderpartialextensions.renderpartial(v=vs.118).aspx[^]

https://msdn.microsoft.com/en-us/library/system.web.mvc.html.renderpartialextensions_methods(v=vs.118).aspx[^]

http://stackoverflow.com/questions/5248183/html-partial-vs-html-renderpartial-html-action-vs-html-renderaction[^]

Partial View in ASP.NET MVC 4[^]

http://stackoverflow.com/questions/23801677/what-is-difference-between-html-renderpartial-common-cshtml-and-html-rende[^]

Thanks.