There is no exact equivalent or equally brief English term but you get closer if you use the term PERMISSION, or either LICENSE or EASEMENT. The choice between the latter two will depend on the terms and conditions of the particular legal relationship of lessor and lessee. I think it is important to use the standard property law terminology in the translation. The Hungarian "engedély" in this context should be one of the above three: "permission" - "license" or "easement" (probably not in this case). I do not recommend using "authorization" or "permit."

This PERMISSION can be called the OWNER'S permission or the LESSOR'S permission, sometimes the LICENSOR'S permission. The reference below explains the two common types of permissions granted by a real property owner for the use of property for a specific purpose. In your context, this specific use is to use the real property's address as business address (székhely).

"Sometimes a landowner will give someone permission to use part of his or her property for a specific purpose. Such permission may be either an easement or a license.
An easement is formal permission, granted in writing by deed or similar document, to use another’s property. An easement runs with the land, meaning it remains valid even though the property involved is rented, mortgaged, sold, or transferred through a succession of owners.
Normally, an easement is automatically canceled when it is no longer used for the specific purpose for which it was granted. Easements are commonly granted to utility companies to install and maintain water, sewer, gas, electric, and telephone and cable lines across private property. Sometimes an owner whose property has no entryway (ingress) or exit (egress) will acquire an access easement across adjoining property.
A license is informal permission to use another’s property. It may be in writing, but is more often oral and may be implied from the conduct of the parties. Licenses do not run with the land, so that the holder of a license cannot sell or otherwise transfer it to someone else. Also, the property owner can terminate a license at any time. A typical example of a license would be oral
permission to hunt on an individual’s property.
Because an easement is a genuine interest in property while a license is not, a land dispute may arise about what kind of permission was given. If the court decides that an easement was granted, the permission is an enforceable property right, whereas if the court decides that only a license was granted, then no property right is involved.of, say, one-eighth of the value of any oil or natural gas brought to the surface."
http://www.ohiobar.org/General Resources/Law_and_You_08.pdf

Other references you might find useful:

Commercial Leases
...Whether you're talking about a residential lease, that is, a lease for a place to live, or a commercial lease, a place to work, the basic idea is the same: a property owner, or the "landlord" or "lessor," lets a "tenant" or "lessee" use the property in exchange for payment of some sort by the tenant, usually rent money....
http://real-estate.lawyers.com/commercial-leasing/Commercial...

Rental vs. license to use real estate

License to use
A license to use real estate merely grants a right to use the real property. It does not confer exclusive dominion or control over the property. Under a license to use real estate, the owner typically controls such things as lighting, heating, cleaning, repairing, and opening and closing the premises.
http://dor.wa.gov/content/getaformorpublication/publicationb...

Temporary License for Use of Real Property
http://www.soartmss.com/sitebuildercontent/sitebuilderfiles/...