Question about secure file transfer

Hi all, I am running a large scale business and some time I have to transfer large and very important data files to my business partner. I fear about my data because there are many of my business competitors who will definitely try to steal my important data. So there is huge amount of risk involved in sharing my important data on Internet. I recently heard about secure file transfer technique from my friend who is working in well established software company. Does anyone have any idea about what is Secure File Transfer (SFT) service and how does it work?