The 16-bit unsigned integer values is a representation of specific characters and since it is a set of elements, you are able to grab specific characters within a string with [] notation as you would a list. Ex:

const string = 'john doe';
console.log(string[3]) // Will print 'n' as it is the 3rd index characters (starts at 0)

it just means that a string is an "array-like" object with each character available in a similar manner to an array element. Each of those characters are stored as a UTF-16 value.

// The following is one string literal:
let s = "ABCDEFG";

console.log(s);

// But it's also an array-like object in that it has a length and can be indexed
console.log("The length of the string is: ", s.length);
console.log("The 3rd character is: ", s[2]);

// And we can see that the characters are stored as separate UTF-16 values:
console.log(s.charCodeAt(2));

As I understood:

1. unsigned means not + or -.
2. 16 bit means 2^16 number of elements/characters can represent.
3. set of Integers mean to represent a String use multiple integers (1 or more).

Therefore this means to represents a string js use set of numbers (each numbers is a 1 of 2^16 numbers because no float numbers and no positive/negative representation).

Note: to understand more read about utf-16

Reference:https://www.ibm.com/docs/en/i/7.2?topic=unicode-utf-16