A lease to which the debtor is a party and whose term has not expired. A debtor may assume, or assume and assign, only those leases that are unexpired. The bankruptcy filing does not extend the term of a lease.
The Code pointlessly adds the adjective “unexpired” when referring to lease but not to executory contracts.
Bankruptcy Code § 365. See also Assumption and Assignment of Executory Contracts and Unexpired Leases, Rejection of Executory Contracts and Unexpired Leases.