Antibacterial soap is any cleaning product to which purportedly antibacterial chemicals have been added. These chemicals are thought to kill bacteria. They do not kill viruses.

In an informal survey of liquid hand and body soaps at the supermarket, most contained antibacterial chemicals. Triclosan is a common ingredient. Since there are a great many different kinds of bacteria, effectiveness against any given type of bacteria does not ensure that it is effective against unrelated types of bacteria.

Overuse of chemicals like triclosan may cause sensitive bacteria to evolve resistance to its antibacterial action. Should we discover an antibiotic that works similar to triclosan, it's effectiveness to combat infections will be reduced because people will be hosting resistant bacteria already due to their use of soaps containing triclosan.

In those studies that have examined the issue, simply washing thoroughly with plain soap is sufficient to reduce bacteria and is effective against viruses also.

Some soaps contain tetrasodium EDTA which is a chelating agent that sequesters metals that the bacteria require in order to grow. Other microbes also require metals and so it is actually an anti-microbial agent that is widely used even as a preservative. It appears to be fairly harmless in the environment.

There are other chemicals used in cleaning agents to kill germs but their purpose seems more directed at marketing an untested feature than in promoting hygiene.