Section 1. The following words as used in this chapter, unless the context otherwise requires, shall have the following meanings:
''Board of aldermen'' or ''selectmen'' includes the board or other authority exercising the powers of a board of aldermen or of selectmen; but nothing herein shall be construed as affecting the veto power of a mayor of any city.
''Department'', the department of public utilities.
''Public way'', any way laid out by public authority.
''Railroad'', a railroad or railway of the class usually operated by steam power.
''Railroad corporation'', the corporation which lays out, constructs, maintains or operates a railroad of the class usually operated by steam power.
''Railroads and railways'', all railroads and railways except tramways in mines and marine railways.