Did you click on the link (part of the text that you quoted in your response)?

In short, an interpreter just reads the source code and interprets (executes) it directly. A JIT compiler actually compiles the source code, either into an intermediate language (this is what Java does when it JIT compiles into bytecode that runs on the JVM virtual machine), or to machine code (this is what Dart does with its JIT compiler; it compiles directly into ARM machine code). But in JIT, this compilation is done after the program starts running, instead of being done at development time (AOT). It is called JIT (just in time) because it happens during runtime when the execution encounters a section that has not yet been compiled. One advantage of JIT is that for a dynamic language (like JavaScript), more can be known about the actual types, which can allow better code to be produced.