int is a primitive data type in c# .net language
System.Int32 refers the base class of int in c# .net
This System.Int32 is base type for all the .net languages such as integer in vb.net and also other all the .net languages
to find out the base type of a data type we use typeof constant
as like below
Console.WriteLine(typeof(int))
typeof is a constant which will return the base type of the given data type