This used to be a very simple question and it had a simple answer. It cost what you paid.

Now along comes one of my most popular contributors Efrata Denny. His Volume 2 issue 45 gives us 10 different types.

Some of the examples and definitions have been known for a long time (fixed, variable, direct and indirect). Some are newish (sunk, opportunity, marginal, life cycle & hidden). The last one could be considered newer depending on your interests, company, location and perhaps your age (social)