Neither, really. It means "working", in a technical sense. "Don't use the old recorder, it isn't operative". Something is either operative or not, whereas things can have different degrees of efficiency or effectiveness. It's not a commonly used word, as it is mostly used in technical language. It can also be a noun, meaning a person that does a certain job.

I think the most common use of the word "Operative" would be a person who is secretly working for another organization. A spy would be an operative. Example; The government had operatives in the airport, at the restaurant, and at the train station. I would understand this word used to describe a machine that is functioning. The old tape recorder is still operative.

Thank you, Ms. Twala

It means effective. Being effective is about doing the right things, while being efficient is about doing things right (I hope this helps Sultan! :))

Lexico gives you this "operative, adjective 1 Functioning or having effect. ‘the transmitter is operative’ 1.1 attributive (of a word) having the most significance in a phrase or sentence. ‘I was madly—the operative word—in love’ 2 attributive Relating to surgery. ‘wounds needing operative treatment’ noun 1 A worker, especially one in a manufacturing industry. ‘the operatives clean the machines at the end of every shift’ 2 North American A secret agent or private detective. ‘a CIA operative’ "