Section 1. Unless a different meaning clearly appears from the context, the following terms, wherever used in this chapter, shall have the following meanings:—

''Blighted open area'', a predominantly open area which is detrimental to the safety, health, morals, welfare or sound growth of a community because it is unduly costly to develop it soundly through the ordinary operations of private enterprise by reason of the existence of ledge, rock, unsuitable soil, or other physical conditions, or by reason of the necessity for unduly expensive excavation, fill or grading, or by reason of the need for unduly expensive foundations, retaining walls or unduly expensive measures for waterproofing structures or for draining the area or for the prevention of the flooding thereof or for the protection of adjacent properties and the water table therein or for unduly expensive measures incident to building around or over rights of way through the area, or for otherwise making the area appropriate for sound development, or by reason of obsolete, inappropriate or otherwise faulty platting or subdivision, deterioration of site improvements or facilities, division of the area by rights of way, diversity of ownership of plots, or inadequacy of transportation facilities or other utilities, or by reason of tax and special assessment delinquencies, or because there has been a substantial change in business or economic conditions or practices, or an abandonment or cessation of a previous use or of work on improvements begun but not feasible to complete without the aids provided by this chapter, or by reason of any combination of the foregoing or other conditions; or a predominantly open area which by reason of any condition or combination of conditions which are not being remedied by the ordinary operations of private enterprise is of such a character that in essence it is detrimental to the safety, health, morals, welfare or sound growth of the community in which it is situated.

''Decadent area'', an area which is detrimental to safety, health, morals, welfare or sound growth of a community because of the existence of buildings which are out of repair, physically deteriorated, unfit for human habitation, or obsolete, or in need of major maintenance or repair, or because much of the real estate in recent years has been sold or taken for non-payment of taxes or upon foreclosure of mortgages, or because buildings have been torn down and not replaced and in which under existing conditions it is improbable that the buildings will be replaced, or because of a substantial change in business or economic conditions, or because of inadequate light, air, or open space, or because of excessive land coverage, or because diversity of ownership, irregular lot sizes or obsolete street patterns make it improbable that the area will be redeveloped by the ordinary operations of private enterprise, or by reason of any combination of the foregoing conditions.

''Sub-standard area'', an area wherein dwellings predominate which, by reason of dilapidation, overcrowding, faulty arrangement or design, lack of ventilation, light, or sanitation facilities, or any combination of these factors, are detrimental to safety, health, morals, welfare or sound growth of a community.

''Construct'', ''construction'', and ''erect'' shall include the renovation, rehabilitation or remodeling of buildings or structures.

''Housing board'' or ''board'', the department of housing and community development.

''Project'', any undertaking consisting of the construction in a blighted open, decadent or sub-standard area of decent, safe and sanitary residential, commercial, industrial, institutional, recreational or governmental buildings and such appurtenant or incidental facilities as shall be in the public interest, and the operation and maintenance of such buildings and facilities after construction. A ''project'' may include as incidental thereto any one or more of the following:— (a) acquisition and assembly of the land (and buildings and structures and other improvements thereon, if any) within a blighted open, decadent or sub-standard area; (b) clearance of the land within a blighted open, decadent or sub-standard area; (c) acquisition, assembly and clearance of land, buildings or structures not in themselves blighted, decadent, or sub-standard if their inclusion is necessary for the clearance, redevelopment, reconstruction or rehabilitation of a blighted open, decadent or sub-standard area; and (d) installation, construction, and reconstruction of public and private ways, public utilities and services, and site improvements essential to the preparation of a blighted open, decadent or sub-standard area for beneficial development or redevelopment.

''Zoning ordinance or by-law'', any special statute establishing zoning regulations in one or more cities, towns or districts, or any ordinance or by-law adopted under chapter forty A or corresponding provisions of earlier laws.

''Mayor'', the duly elected mayor of the city in all cities except those having a Plan D or a Plan E charter and in cities having a Plan D or a Plan E charter, the city manager.