Infrastructure maintenance. Not terribly exciting to think about, especially when there are far sexier topics like war, gun control, global warming, universal health care, No Child Left Behind, illegal immigrants, etc. It's the daily teeth brushing aspects of having a structure that does something useful, like eating tasty food.
A structure only remains in good working order when all of its parts, down to the smallest ones, are also all in good working order. Infrastructure maintenance means repairing or replacing the parts that are broken, and resting or recuperating the parts that are human. It's a basic necessity that must be amply budgeted for - for if one neglects to put in the proper amount of time and money, if one treats it like a luxury that can be cut, sooner or later one will either wind up paying the entire accumulated cost at once (with compound interest), or one will no longer have the structure.
This applies to all sorts of things. Teeth. Roads. Labor. Public education. Health. Environment. Security. Nearly all of which are themselves parts of larger infrastructures.