Declaration means that variable is only declared and memory is allocated, but no value is set.
However, definition means the variables has been initialized.
The same works for variables, arrays, collections, etc.
Declaring a variable.
Let’s define and assign a value.
x = 10;
Declaring an array.
int  n // declaring int n= new int; // initializing
Let’s assign a value.
n = 100; n = 200