initialize is the term commonly used with variables whenever u assign a value to it before executing.
example:
obj = 1obj = "foo"
instantiation refers to assigning an Object to a class(which in turn act as the reference to variables and methods/functions of that class).
example:
Dim obj As New Object()
reference: https://www.quora.com/What-is-difference-between-Instantiate-and-Initialize-in-programming