Assuming there are two dice or two rolls of the same die, there are 36 possible outcomes from 1-1 to 6-6.
There are three ways the absolute difference is 3 between the two is 3: 1-4, 2-5, 3-6. But we can also have 4-1, 5-2, 6-3. So that's 6 out of 36 or 1/6.