Framework & Library
Generally Both frameworks and libraries are code written by someone else that is used to help solve common problems. A framework inverts the control of the program, It tells the developer what they need. A library doesn’t. Programmer calls the library where and when they need it. The degree of freedom a library or framework gives the developer will dictate how “opinionated” it is.
Plug-in is a piece of software that adds new features or extends functionality on an existing application. Commonly used on websites that are built with CMS.