What is Extended Coverage?

Legal Definition
Extended coverage is a term used in the property insurance business. All insurance policies have exclusions specific causes of loss (also called "perils") that are not covered by the insurance company. An extended coverage endorsement (EC) was a common extension of property insurance beyond coverage for fire and lightning. Extended coverage added insurance against loss by the perils of windstorm, hail, explosion, civil commotion, riot and riot attending a strike, aircraft damage, vehicle damage, and smoke damage.

The endorsement has been largely supplanted by what is referred to as "basic" causes-of-loss form first introduced by Insurance Services Office in 1986 as part of its simplified language revisions. The basic form includes most of the perils previously provided by fire and extended coverage and it adds vandalism and malicious mischief, sprinkler leakage damage, sinkhole collapse, and volcanic action. Coverage can also be extended on scheduled personal articles or applied as extensions to personal umbrella liability or extended title.

Broader coverage is available in "broad form" and "special form" causes-of-loss forms. Broad form adds three additional perils plus collapse due to certain causes. Special form covers almost all risks of loss except those that are specifically excluded.
-- Wikipedia
Legal Definition
The amount covered by the current insurance under normal circumstances. It is bought to help cover what is left and covers all possibe loss.