Foundations: What do you mean by "dirt foundation"?

[Julie Taylor]

I've heard a few people, in particular from the Pittsburgh area, mention that they will never again by a house with a "dirt foundation, often citing that it is not possible to perform repairs.  To date, no one has been able to explain exactly what they mean by the phrase "dirt foundation".  I am familiar with homes that are built with piers setting atop poured concrete footers, homes built on full basements (both block and poured wall), and also homes built on concrete slabs that are poured onto the ground. Can anyone tell me what is meant by a "dirt foundation"?  Is it that the house still has piers or posts, but they were never set atop poured concrete footers for support?  Or is it something else altogether?  Any assistance, and maybe even photos, will be greatly appreciated!  Thank you in advance.