Definition of roll-on:
(adj) :
(of deodorant, etc.) Applied by means of a ball that can be rotated to pick up liquid from the inner reservoir.
(n) :
A cosmetic product (especially a deodorant) applied by means of a ball at the head of a container, which rolls the product on to the skin etc.
(n) :
(dated, often in the plural) A type of corset which is rolled on to the body.