In legal terms, being reduced to a peppercorn means the value has been reduced to zero or a nominal amount. The reason why it's referred to as a peppercorn is because for a contract to be legally binding, you can't have a value of zero. However, the value doesn't have to be a number, so to get around this and to ensure that the lease document is still valid, a peppercorn was used to illustrate this. When you get a lease extension, your ground rent will be reduced to a peppercorn.