ECMAScript 3 published in 1999. No changes made to the ECMAScript standard for 10 years after that.
ECMAScript 5 released in 2009
In 2015 the committee responsible for drafting ECMAScript specs decided to move to a yearly model for defining new standards. That’s why the 6th edition of ECMAScript, ES6, is also known as ECMAScript 2015 or ES2015
ES7, thus, will also be known as ECMAScript 2016 or ES2016