What are exploits?
An exploit is a piece of software, a chunk of data, or sequence of commands that take advantage of a bug, glitch or vulnerability in order to cause unintended or unanticipated behavior to occur on computer software, hardware, or something electronic (usually computerized). This frequently includes such things as violently gaining control of a computer system or allowing privilege escalation or a denial of service attack.
Many exploits are designed to provide superuser-level access to a computer system. However, it is also possible to use several exploits, first to gain low-level access, then to escalate privileges repeatedly until one reaches root.
Normally a single exploit can only take advantage of a specific software vulnerability. Often, when an exploit is published, the vulnerability is fixed through a patch and the exploit becomes obsolete for newer versions of the software. This is the reason why some blackhat hackers do not publish their exploits but keep them private to themselves or other malicious crackers. Such exploits are referred to as 'zero day exploits' or '0day exploits' and to obtain access to such exploits is the primary desire of malicious attackers.
There are automated exploitation systems such as CANVAS and Metasploit that include many exploits, an automated exploitation system, and a exploit development framework to malicious attackers/penetration testers/security professionals.