A more thorough explanation:

The Lamb-Weston rule is a doctrine in insurance that applies when two insurance policies provide coverage for the same loss, and each policy contains an other-insurance clause that creates a conflict in the order or apportionment of coverage. In such cases, both other-insurance clauses are disregarded, and liability is prorated between the insurers.

For example, suppose a person has two insurance policies that cover their car, and both policies have an other-insurance clause. If the car is damaged in an accident, the Lamb-Weston rule would apply, and both insurers would be responsible for paying a portion of the damages.

The Lamb-Weston rule was established in the case of Lamb-Weston, Inc. v. Oregon Auto. Ins. Co., where the court ruled that both insurers should share the liability for a loss when their policies conflicted with each other.