wht is the difference between IBM Websphere portal and jsp

Hi experts , wht is the difference between IBM Websphere and jsp ?
I found some jobs asking for web developer in IBM Websphere Portal , then I started to know and take a look at IBM Websphere portal, so what I understand is that it is one way to develop web pages
it is like ASP or PHP

please tell me which one is better , and what is the difference , why some jobs want in that kind of web developments

thanks a lot