"Clutch slippage" refers to a situation where the connection between the engine and the wheels in a vehicle becomes weak or loose, causing the engine to rev up without effectively transferring power to the wheels. Full definition
Those cars were fitted with LC2, which was effectively not a launch control system at all, allowing only 2000 or so rpm of clutch slippage before making its way off the line. (automobilemag.com)
Road test the vehicle and monitor TCC % solenoid command state — duty cycle and TC SLIP ACT torque converter clutch slippage — rpm, while in 2nd, 3rd or 4th gear with a TCC % reading 0. (autoserviceprofessional.com)
To avoid this shifts from lower gears must be done extra gently, to allow more clutch slippage. (mechanics.stackexchange.com)