16 CFR 1309.2: Definition.

Crib bumper:

(1) Means any material that is intended to cover the sides of a crib to prevent injury to any crib occupant from impacts against the side of a crib or to prevent partial or complete access to any openings in the sides of a crib to prevent a crib occupant from getting any part of the body entrapped in any opening;

(2) Includes a padded crib bumper, a supported and unsupported vinyl bumper guard, and vertical crib slat covers; and

(3) Does not include a non-padded mesh crib liner.