3/1 is a simple triple time, similar to 3/4 or 3/2, meaning that it would contain three beats per measure: 1 te 2 te 3 te and so on.
Although I don't think it would be very practical, 3/1 could also be interpreted as compound single, similar to 3/8, meaning it would have one beat per measure with three subdivisions: 1 la li and so on.