Generally, an exploit is a vulnerability of a software applicaiton that can be used to place a virus or malware on a PC or smartphone. If this exploit is not yet (publicly) known, it is called a zero-day exploit. Although software companies such as Google pay bug bounties for finding exploits, zero-day exploits are also traded on the black market; the prices offered on the black market for zero-day exploits are often higher than the bug bounties offered by software companies.
