Overhearing something accidentally isn't, but purposefully putting yourself in proximity so you have a chance for that is espionage and possibly social engineer

Overhearing something accidentally isn't, but purposefully putting yourself in proximity so you have a chance for that is espionage and possibly social engineering (depending on whether you're just near or playing yourself off as part of a similar group). In many ways, this is close to the original term of hacking, which is less about computers and more about circumvention of restrictions and security.