int means integral data type, that is a number that does not have any fractional part. If it helps, in Math it would be Z. Such numbers are ..., -2, -1, 0, 1, 2, ...
In C, you could write the following code:
#include <stdio.h>
int main()
{
int age;
printf("Enter your age: ");
scanf("%d", &age);
printf("You are %d years old.\n", age);
return 0;
}