Leasehold Improvement

Improvements on a leased asset that increase the value of the asset.

Investopedia Says:
A leasehold improvement is classified as an asset that must be depreciated over time.

Fixtures, attached to real estate that are generally acquired or installed by the Tenant. Upon expiration of the Lease the tenant can generally remove them, provided such action does not damage the property or conflict with the lease. For example, the cabinets, light fixtures, and window treatments of a retail store in a leased building are leasehold improvements. See also Tenant Fixtures.

Fixtures attached to real estate that are generally acquired or installed by the Tenant. Upon expiration of the Lease the tenant can generally remove them, provided such action does not damage the property nor conflict with the lease.
Example: Cabinets, light fixtures, and window treatments of a retail store in a leased building are leasehold improvements.

Upgrading made by a lessee to leased property. Examples are paneling and wallpapering. These improvements revert to the lessor at the expiration of the lease term. As improvement costs are incurred under an operating lease, the leasehold improvement account is charged. The leasehold improvement is amortized to expense over the shorter of the life of the improvement or the remaining lease term. If there is a lease renewal option and the prospect of renewal cannot be predicted with certainty, the amortization period should be the original lease term rather than the longer possible term. However, the amortization expense on a leasehold improvement is not tax deductible. Leasehold improvement is usually considered an Intangible Asset, because the lessee does not own the leased property. However, some companies show it under the property, plant, and equipment section of the balance sheet.