What is Landlord?

Legal Definition
A landlord is the owner of a house, apartment, condominium, land or real estate which is rented or leased to an individual or business, who is called a tenant (also a lessee or renter). When a juristic person is in this position, the term landlord is used. Other terms include lessor and owner. The term landlady may be used for women owners, and lessor applies to both genders.
-- Wikipedia
Legal Definition
He who rents or leases real estate to another.

2. He is bound to perform certain duties and is entitled to certain rights, which will here be briefly considered. 1st. His obligations are, 1. To perform all the express covenants into which he has entered in making the lease. 2. To secure to the tenant the quiet enjoyment of the premises leased; but a tenant for years has no remedy against his landlord, if he be ousted by one who has no title, in that case the law leaves him to his remedy against the wrong doer. Y. B. 22 H. VI. 52 b, and 32 H. VI. 32 b; Cro. Eliz. 214; 2 Leon. 104; and see Bac. Ab. Covenant, B. But the implied covenant of quiet enjoyment may be qualified, and enlarged or narrowed according to the particular agreement of the parties; and a general covenant of quiet enjoyment does not extend to wrongful evictions or disturbances by a stranger. Y. B. 26 H. VIII. 3 b. 3. The landlord is bound by his express covenant to repair the premises, but unless he bind himself by express covenant the tenant cannot compel him to repair. 1 Saund. 320; 1 Vent. 26, 44; 1 Sed. 429; 2 Keb. 505; 1 T. R. 812; 1 Sim. R. 146.

3. His rights are, 1. To receive the rent agreed upon, and to enforce all the express covenants into which the tenant may have entered. 2. To require the lessee to treat the premises demised in such manner that no injury be done to the inheritance, and prevent waste. 3. To have the possession of the premises after the expiration of the lease. Vide, generally, Com. L. & T., B. 3, c. 1; Woodf. L. & T. ch. 10; 2 Bl. Com. by Chitty, 275, note; Bouv. Inst. Index, h. t.; 1 Supp. to Ves. Jr. 212, 246, 249; 2 Id. 232, 403; Com. Dig. Estate by Grant, G 1; 5 Com. Dig. tit. Nisi Prius Dig. page 553; 8 Com. Dig. 694; Whart. Dig. Landlord & Tenant. As to frauds between landlord and tenant, see Hov. Pr. c. 6, p. 199 to 225.
-- Bouviers Law Dictionary
Legal Definition
He of whom lands or tenements are holdeu. He who, being the owner of an estate in land, has leased the same for a term of years, on a rent reserved, to another person, called the "tenant." Jackson v. Harsen, 7 Cow. (N. Y.) 326, 17 Am. Dec. 517; Becker v. Becker, 13 App. Div. 342, 43 N. Y. Supp. 17. When the absolute property in or fee-simple of the land belongs to a landlord, he is then sometimes denominated the "ground landlord," in contradistinction to such a one as 'is possessed only of a limited or particular interest in land, and who himself holds under a superior landlord. Brown.
See also
-- Black's Law Dictionary
Legal Definition
One who leases land to another. See 7 Cow. (N. Y.) 323, 17 Am. Dec. 517.
-- Ballentine's Law Dictionary