VMCA? I’m not familiar with this abbreviation.
The minimum speed at which an aircraft is directionally and laterally controllable with one engine inoperative and windmilling. It also involves flying the aircraft with not more than a 5 degree angle of bank towards the inoperative engine, full power on the remaining engine, landing gear retracted and flaps in the takeoff position.
In real terms below this speed the aircraft cannot be kept either straight or from rolling towards the inoperative engine. You will run out of rudder and aileron and the aircraft will turn into a smoking hole in the ground.
The decision to abandon flight after takeoff but before blue line is contentious with some pilots. A Cessna "Pilot Safety and Warning Supplements" booklet that I have recommends retracting the undercarriage and continuing the flight (also doing the PHASE 1 actions!). A friend of mine who has many thousands of hours in general aviation multi-engine aircraft also uses this. The company I work for uses blue line as its go/no go speed and the speed where the undercarriage is retracted. Given the conditions where we fly it is unlikely that an aircraft would be saved by trying to fly it away with an engine failure below blue line.