Earthquake insurance covers damage caused by an earthquake. It matters because standard homeowners, renters, and condo policies exclude earthquake damage everywhere, so it must be bought as a separate policy or added by endorsement.
Earthquake coverage usually carries a percentage deductible (a percent of the dwelling limit), which is often higher than a standard deductible.
Example: a home suffers foundation and chimney damage in a quake. A standard homeowners policy pays nothing because earthquake is excluded; a separate earthquake policy or endorsement is what responds.
Related: percentage deductible, endorsement, peril, dwelling coverage. See the homeowners insurance overview.