As others have said there is a sound engineering 'trick' in which you pan an instrument or sound hard to one side and then mix in the same track panned hard to the other side but 180˚ out of phase. At the mixing desk it pops the track right outside of the speakers and leaves lots of space in the centre of the mix... which is very handy in a lot of cases. The effect only really works on a stereo loudspeakers, it doesn't work on headphones and in mono the instrument or sound will be greatly attenuated as the out of phase signal is summed with the original. In most cases an engineer doesn't know how a track will be listened to (with the exception of vinyl) so effects like these are used pretty sparingly.
Many systems are able to render a soundstage wider than the speakers even when there are no 'tricks' like this in play... I enjoy a number of recordings made with a single stereo pair of microphones that have a huge soundstage. In my experience it's usually down to the recording and the loudspeakers. An average room is capable of a wide soundstage as long as there is enough distance between the loudspeaker and the side walls to avoid flutter echos. You can put absorbers at the first reflection points (imagine the wall is a mirror and you're looking at the reflection of your loudspeaker from your listening position) to tame the worst of these.
Many systems are able to render a soundstage wider than the speakers even when there are no 'tricks' like this in play... I enjoy a number of recordings made with a single stereo pair of microphones that have a huge soundstage. In my experience it's usually down to the recording and the loudspeakers. An average room is capable of a wide soundstage as long as there is enough distance between the loudspeaker and the side walls to avoid flutter echos. You can put absorbers at the first reflection points (imagine the wall is a mirror and you're looking at the reflection of your loudspeaker from your listening position) to tame the worst of these.