Literal equestrian tool worn on a rider's heel to urge a horse forward.
The cowboy spurred his horse and galloped away.
spurring on; impetus; acceleration
Figurative use: something that stimulates or accelerates a process, often in the pattern ～に拍車をかける.
The introduction of new technology spurred changes in the industry.
His remark added to her anxiety.
The jockey spurred the horse's flank to make it run.
The rapidly accelerating urban development is causing problems.
促進 refers to deliberate, steady promotion of something, whereas 拍車 evokes a sudden, dramatic acceleration like spurring a horse.
拍車（をかける）means to accelerate a trend, while 抑制（する）means to hold it back or restrain it.
拍車 (spur) and 拍手 (clapping/applause) share the kanji 拍 and similar sound, but refer to completely unrelated things.
拍車 is counted with 対 because riding spurs are made and worn as a matched pair, one on each boot.
個 can be used to count a single 拍車 when referring to just one spur rather than the pair.
Compound of 拍 (beat, clap) and 車 (wheel, vehicle). Originally referred to a spur used in horse riding, later extended figuratively to anything that provides impetus.