What is Improvement?

Legal Definition
Improvement is the process of a thing moving from one state to a state considered to be better, usually through some action intended to bring about that better state. The concept of improvement is important to governments and businesses, as well as to individuals.
-- Wikipedia
Legal Definition
Rights. An addition of some useful thing to a machine, manufacture or composition of matter.

2. The patent law of July 4, 1836, authorizes the granting of a patent for any new and useful improvement on any art, machine manufacture or composition of matter. Sect. 6. It is often very difficult to say what is a new and useful improvement, the cases often approach very near to each other. In the present improved state of machinery, it is almost impracticable not to employ the same elements of motion, and in some particulars, the same manner of operation, to produce any new effect. 1 Gallis. 478; 2 Gallis. 51. See 4 B. & Ald. 540; 2 Kent, Com. 370.
-- Bouviers Law Dictionary
Legal Definition
A valuable addition made to property (usually real estate) or an amelioration in its condition, amounting to more than mere repairs or replacement of waste, costing labor or capital, and intended to enhance its value and utility or to adapt it for new or further purposes. Spencer v. Tobey, 22 Barb. (N. Y.) 269; Allen v. McKay, 120 Cal. 332, 52 Pan. 828; Simpson v. Robinson, 37 Ark. 132. In American land law. An act by which a locator or settler expresses his intention to cultivate or clear certain land; an act expressive of the actual possession of land; as by erecting a cabin, planting a corn-field, deadening trees in a forest; or by merely marking trees, or even by plling up a brush-heap. Burrill. And see In re Leet Tp. Road, 159 Pa. 72, 28 Atl. 238; Bixler v. Baker, 4 Bin. (Pa.) 217. An "improvement," under our land system, does not mean a general enhancement of the value of the tract from the occupant's operations. It has a more limited meaning, which has in view the population of our forests, and the increase of agricultural products. All works which are directed to the creation of homes for families, or are substantial steps towards bringing lands into cultivation, have in their results the special character of "improvements," and, under the land laws of the United States and of the several states, are encouraged. Sometimes their minimum extent is defined as requisite to convey rights. In other cases not. But the test which runs through all the cases is always this: Are they real, and made bona fide, in accordance with the policy of the law, or are they only colorable, and made for the purpose of fraud and speculation? Simpson v. Robinson, 37 Ark. 137. In the law of patents. An addition to, or modification of, a previous Invention or discovery, intended or claimed to Increase its utility or value. See 2 Kent, Comm. 366-372. And see Geiser Mfg. Co. v. Frick Co. (C. C.) 92 Fed. 191; Joliet Mfg. Co. v. Dice, 105 111. 650; Schwarzwaelder v. Detroit (C. C.) 77 Fed. 891; Reese's Appeal, 122 Pa. 392, 15 Atl. 807; Rheem v. Holliday, 16 Pa. 352; Allison Bros. Co. v. Allison, 144 N. Y. 21, 38 N. E. 956. See Local improvement.
-- Black's Law Dictionary
Legal Definition
A term used in leases, of doubtful meaning. It would seem to apply principally to buildings, though generally it extends to the amelioration of every description of property, whether real or personal; but, when contained in any document, its meaning is generally explained by other words. 1 Chit Gen. Pr. 174.
-- Black's Law Dictionary
Legal Definition
Additions to or alterations of property which increase its value.
-- Ballentine's Law Dictionary