The length of time until a financial contract expires. This is different than maturity which is the length of the original contract.
For example, a mortgage could be 30 years with a maturity in 2040. The tenor for this debt is 18 years as of this writing.
Tenor is vital for matching assets especially in swaps. Financial institutions seek to align assets based upon their tenor. This means that 5 year and 20 year contract (bonds) could be pair together if the tenors match up.