^^Primitive value.

primitive value

Data that is directly represented at the lowest level of the language.
A JavaScript primitive value is a member of one of the following types:
undefined, null, Boolean, number, or string.
The following examples show some primitive values. 
a=true               // Boolean primitive value
b=42                 // number primitive value
c="Hello world"      // string primitive value
if (x==undefined) {} // undefined primitive value
if (x==null) {}      // null primitive value