What do you call a cylinder with a hole down the center?

Solution 1:

A solid cylinder with an axial hole is still a cylinder. If the length of the cylinder is very much less than the diameter and the bore is small compared to the diameter it is a washer. If the length is much larger than the diameter, and especially if the bore is nearly as large as the cylinder diameter it is a tube.

Solution 2:

Cylinder -Wiki

Open Cylinder

A cylinder -with the generating lines perpendicular to the bases, with its ends closed to form two circular surfaces- with a hole perpendicular to its base, is a right circular, open cylinder.
Its function tells us if it's a pipe, washer, bearing, beer can, ect.

Google's 4th picture hit for open cylinder:

Solution 3:

Colloquially, i'd just call it a hollow cylinder.