1. When used in this chapter, unless the context or subject matter otherwise requires, the terms "state department of transportation," "state transportation department," "department of transportation," "transportation department," "department," "state commissioner of transportation," "commissioner of transportation," "commissioner," and "state engineer," shall each be deemed to refer to and to mean the state department of transportation and the state commissioner of transportation, respectively.2. The term "county engineer" or "county superintendent," when so used, shall mean the county engineer of highways or county superintendent of highways respectively.3. The term "town superintendent," when so used, shall mean the town superintendent of highways.4. A highway within the meaning of this chapter shall be deemed to include necessary sluices, drains, ditches, waterways, embankments, retaining walls and culverts having a width of opening of twenty feet or less except as provided in section two hundred and thirty, and also the approaches of any bridge or culvert beginning at the back of the abutments. The pavement over any such bridge or culvert may also be included as a part of the highway provided such pavement is separated from such structure by an earth fill.5. An "infant", as used in this chapter, shall mean any person who has not attained the age of eighteen years.