imaginary line
curved or straight line with a well-defined physical location, that is not itself a physical object
Line of scrimmage
imaginary transverse line in American football, beyond which a team cannot cross until the next play has begun
chord
imaginary straight line joining the leading and trailing edges of an aerofoil
oche
toe line in darts
sightline
in architecture, urban design, and landscape architecture, a line offering unobstructed, framed views of a point of interest
terminator
moving line that separates the illuminated day side and the dark night side of a planetary body
camber
asymmetry between the two acting surfaces of an airfoil, or an imaginary line between the two surfaces
lines of non-extension
notional lines running across the human body along which body movement causes neither stretching or contraction
ground track
path on the surface of the Earth or another body directly below an aircraft or satellite
geographical boundary
line of delimitation or demarcation between geographical units of all types, whether physical or human