An over-the-counter drug can be purchased without a doctor's prescription. The same is true of under-the-counter drugs, but look out: anything that happens under-the-counter is secret and possibly illegal, much like under-the-table payments. It can help you remember the meaning of this phrase if you remember that over-the-counter activities can be seen, while under-the-counter activities can't. Buying a bootleg DVD on the street is another under-the-counter transaction, whereas buying a DVD in a local store is an over-the-counter transaction.