A more thorough explanation:

A memorandum clause is a marine-insurance clause that protects underwriters from liability for injury to goods that are particularly perishable or for minor damages. This clause was first introduced into English marine-insurance policies around 1749. Before that time, the insurer was liable for every injury, no matter how small, that happened to the insured item.

The memorandum clause usually declares that the enumerated articles, and any other articles that are perishable in their own nature, shall be free from average under a given rate, unless general, or the ship be stranded. In other words, the clause exempts certain items from being covered by insurance unless there is a general average or the ship is stranded. This means that all small partial losses, however inconsiderable, are to be borne by a general average, provided they were incurred in a case proper for such an average.

For example, if a shipment of fresh fruit is insured under a marine-insurance policy with a memorandum clause, and some of the fruit spoils during transport, the insurer may not be liable for the loss because the fruit is perishable in nature. Similarly, if a small dent or scratch occurs on a piece of insured cargo during transport, the insurer may not be liable for the damage because it is considered a minor damage.