Aversives are unpleasant consequences that are meant to control and manage behavior. In psychological research these can include bad smells, electric shocks, bad flavors in food or water, and uncomfortable temperatures. In child-rearing these may include time-outs, scolding, loss of privileges, or corporal punishment.
For adults, there are aversives like parking tickets, loss of wages, spousal problems and others. Essentially, an aversive can be be anything that is considered unpleasant and can result in a change in behavior. Aversives are the core component behind aversive conditioning.