What is “accessor function”?

Question

In section 4.3.26 of the Standard ECMA-262 Edition:

Depending upon the form of the property the value may be represented either directly as a data value

Answer 1

"A pair of accessor functions" are the getter and the setter.

Documentation and example:

var o = {}; // Creates a new object

// Example of an object property added with defineProperty with an accessor property descriptor
var bValue = 38;
Object.defineProperty(o, 'b', {
  get: function() { return bValue; },
  set: function(newValue) { bValue = newValue; },
  enumerable: true,
  configurable: true
});