What is the difference between ECMA Script and Javascript?

ECMA script is set of standard rules (set by ECMA international) while JavaScript is implantation of them. So, the JavaScript engine adhere to ECMA standard rules.

ECMAScript is a language specification created by ECMA International, which defines the rules, syntax, and features of a scripting language whereas JavaScript is a programming language that implements the ECMAScript specification. In short, ECMAScript defines the core features and behavior of the language while JavaScript is an implementation of that specification.