Aggie- two a days is when you go to the gym twice in one day. Like, today, I worked with my trainer this am -full body weight lifting. And then at 6pm I will go to cardio.
Most people do two a days when they are training for something or have a goal in mind. For me, I want to lose 2 pounds a week, so I do two a days twice a week to ensure I get all my cardio in! Lovin it!