Grounding is a midterm isolation punishment in which the person punished has his or her movements restricted, or is forbidden to participate in some pleasurable activity. It can occur in various degrees of severity, and last for a wide variety of times.
Grounding does not restrict physical movement as tightly as time-out (in particular corner time), but while these punishments usually last for some minutes, rarely more than an hour, grounding is often given for hours, days or even weeks. So it tends to be used as a light but long-term punishment.
The most classic form of grounding is one in which the person is restricted to a dwelling, and forbidden to leave it (perhaps except for required school or business events). In a stricter form, the person being punished may be restricted to a particular room ("sent to her room"). In a more generalized form, a person might be "grounded from the computer" or "grounded from his bike/car" — that is, forbidden the use of the particular tool or toy — although the latter are strictly speaking not cases of grounding but of removal of privileges.