This is required only if you have a part land, part building lease, whose land portion is 25% or more of the total value, under FAS 13. It is used to calculate the portion of the rent that is considered land rent and therefore always operating, even if the building portion is finance. Unless you're entering old leases for the first time which fit these parameters, the field should be left blank.
If you enter a discount rate, you should set the classification to Sales Type or Direct Financing. If you don't, EZLease will assume Sales Type, but display a warning message at the end of the upload. It's best practice to be explicit. If both the classification and the discount rate are left blank, EZLease will determine the classification based on the input data for the lease.