Answer Description

A hot site is a backup site that is a near mirror of the primary site. In the event of a disruption to the primary site, a hot site can be ready and operating within hours. A cold site can be up within weeks. While a warm site can be up within days.

Wikipedia

A backup site or work area recovery site is a location where an organization can relocate following a disaster, such as fire, flood, terrorist threat or other disruptive event. This is an integral part of the disaster recovery plan and wider business continuity planning of an organization.A backup, or alternate, site can be another data center location operated by the organization, or contracted via a company that specializes in disaster recovery services. In some cases, one organization will have an agreement with a second organization to operate a joint backup site. In addition, an organization may have a reciprocal agreement with another organization to set up a site at each of their data centers. Sites are generally classified based on how prepared they are and the speed with which they can be brought into operation: "cold" (facility is prepared), "warm" (equipment is in place), "hot" (operational data is loaded) – with increasing cost to implement and maintain with increasing "temperature".