Need Understanding

I’m learning PHP. With that said i’m also endeavoring to learn MySQL as well and i have some questions about terminology. First of all what exactly is a php framework? I assume that it is a cms built by someone or some company for the purpose of designing a web site; just not sure? Also is that the best way to go and what frameworks are considered easy to learn and build from? Another question that i have is what is an iframe? And do most php/MySQL sites use them? And last one for now is; is a frame the same thing as an iframe and if not; what is the difference? Thank you in advance for your help!!! :stunned: