The 'enumerable' property flag controls whether a property appears in enumeration operations: 1) When false, the property is hidden from for...in loops, 2) Non-enumerable properties are excluded from Object.keys(), 3) They're also omitted from JSON.stringify() output, 4) They remain accessible directly by name, 5) This flag is useful for hiding metadata or internal implementation details, 6) Most built-in methods on Object.prototype are non-enumerable to avoid cluttering enumeration results, 7) It helps create cleaner, more predictable object iterations.