Other People's Money (OPM) or float basically means that savvy business people arrange to receive cash owe to them at the earliest opportunity and send money that they are obligated to pay others at the last possible moment. When managed well, this results in a cache of money called float.

You can earn interest on your float. The master of float is Warren Buffett because he gets to invest his float consisting of insurance premiums prior to them being paid out to cover insurance claims.

The book mentions variants of OPM such as :

a) Gift certificates - All that amount of Kino vouchers you are hoarding is earning them interest.
b) Traveler's checks - I never used these but folks prefer to keep them rather than redeem them after a trip.
c) Commemorative stamps - No sane collector will use the stamps in the First Day Cover to send actual mail.
d) Celebrity Checks -...