"Zinsbindung" refers to the fixing of an interest rate, usually in the context of a loan (e.g. a mortgage where the interest rate is fixed for a certain period of time), but also when looking at leasing structures. (After all, a leasing contract reflects the economics of the underlying loan.)

If you really have no context (not even a table entry that would allow you to judge if this refers to a time period, or - somewhat less likely, but not impossible - to a rate), I strongly suggest to check this with the (end) customer.