Karma yoga

anarisit karamfalam kareykarm kroti ya.

sa sanyasi sa yogi naniragan cha kirya. — Chapter 6 solaka 1.

In this sloka Shri Krishna tells us the true meaning of Sanyasi a true sanyasi is he who left the fruit of his karmas, he is doing his duties with full interest but is not attached to the fruit what reward he will gain his work. because when we want any reward for our karmas then one thing we can not do our job with fun. because now there at that time we attach to the desire that we will find this thing as the fruit of this task. according to Hindu theory, our next birth happens according to our vassnas ( our wants). and if we want to come out of this circle of birth and death then there should be no any desire left. so according to this sloka if a man is doing his work without the desire of the fruit than he is a real sanyasi.