Hardpack soil is what most of us spend our time riding on. This type of soil is just what its name implies. Hardpacked soil has been packed down either by tires, feet, or just plain mother nature, into a firm layer of dirt that is structurally developed enough to prevent much penetration or deformation from your tires.
Hardpack is the most common soil condition if the weather has been dry, and the trail is in good condition without much loose dirt on top.
Tire traction is usually quite good on hardpack with most tires, but tires designed specifically for it will perform better.
This soil is not quite damp, tacky, or sticky. If it were it would be called tacky soil which is even more fun.
Common Misspellings: Hard Pack
That trail was in good shape, it had some great hardpack sections.