Nested Collections: "immutable" arrays, Clarify independence of inner arrays in nested collections example (#30215)

* Clarify independence of inner arrays in nested collections example

* Rename variable for clarity in immutable nested arrays example

* Clarify section heading for creating nested arrays in mutable context

* Clarify wording for creating non-mutable nested arrays

Author: Bijay-Shre-stha

ruby/basic_ruby/nested_collections.md

@@ -99,17 +99,19 @@ mutable
 
 Changing the value of the first element in the first nested array, causes the first element to change in all three nested arrays! This same behavior will happen with strings, hashes, or any other mutable objects.
 
-<span id='create-immutable-nested-arrays'>Now, let's take a look at an example that omits the second optional argument and instead passes in the mutable value in a block.</span>
+<span id='create-nested-arrays'>Now, let's take a look at an example that omits the second optional argument and instead passes in the mutable value in a block.</span>
 
 ```ruby
-immutable = Array.new(3) { Array.new(2) }
+nested_arrays = Array.new(3) { Array.new(2) }
 #=> [[nil, nil], [nil, nil], [nil, nil]]
-immutable[0][0] = 1000
+nested_arrays[0][0] = 1000
 #=> 1000
-immutable
+nested_arrays
 #=> [[1000, nil], [nil, nil], [nil, nil]]
 ```
 
+Each `{ Array.new(2) }` block creates a new inner array. This means all three inner arrays are **independent objects**. When you modify one, the others stay the same.
+
 Changing the value of the first element in the first nested array does not cause the value to change in any other nested array.
 
 ### Adding and removing elements
@@ -352,7 +354,7 @@ The following questions are an opportunity to reflect on key topics in this less
 - [How do you add data to a nested hash?](#adding-and-removing-data)
 - [How do you delete elements from a nested array?](#remove-elements-nested-array)
 - [How do you delete data in a nested hash?](#deleting-data-nested-hash)
-- [How do you create a new nested array that is not mutable?](#create-immutable-nested-arrays)
+- [How do you create a new nested array that can’t be changed through references to the original one?](#create-nested-arrays)
 - [How do you iterate over a nested array?](#iterating-over-a-nested-array)
 - [How do you iterate over a nested hash?](#methods)