Definition of redlines:
(n) :
The maximum speed, temperature, pressure, etc., at which a device (such as the engine in a car, aircraft, etc.) is designed to operate.
(v) :
(automotive) To run an internal combustion engine to its maximum or maximum recommended speed.
(v) :
To mark a drawing or document for correction or modification.
(n) :
A drawing, document, etc. that has been marked for correction or modification.
(v) :
(Canada, US, urban studies) To deny or complicate access to services (such as banking, insurance, or healthcare) to residents in specific, often racially determined, areas.
(v) :
(audio engineering) To achieve audio levels that will cause clipping (indicated by red in an audio meter).