How about I present it in another way because it depends on what one is talking about.
Imagine you have 1,000,000 coins made up of 60 pennies and 999,999,940 nickels. Your pennies would have a concentration of 60 parts per million (or more specifically, 60 pennies per one million coins) and your nickels would have a concentration of 999,999,940 parts per million.
In terms of a formulated motor oil and let's say a moly additive, 60 ppm represents 60 milligrams of moly per 1000 grams of the formulated motor oil.
Using ppm as a measure of concentration can be confusing because it typically does not indicate if it is dealing with volume, weight, or number of items (like with the coins).
I hope this helps.