Every object has a 'Center of Gravity'.  This is where the average weight of any object (including people) is located.  When we balance, we have to keep our center of gravity supported.  That is to say, we have to 'hold up' our weight!  Whatever is holding up your weight is called your 'Base of Support'.

If you are standing on two feet, then those feet are your base.  If you are standing on one foot, then only that one foot is your base.  If you are sitting, them your bottom is your base.

To stay balanced, we have to keep our center of gravity (our weight) over top of the base of support (whatever is holding us up).

When training patients to balance, one of the first tasks is to get the person to recognize and feel their center of gravity.  Many times, people who have balance problems lose this sense.  This is one reason they fall, as they cannot feel when they are placing their weight outsite of the area that is supporting it!  Sometimes, assistive devices such as canes or walkers help.  But even with a cane or walker, most patients still may benefit from balance training to help reduce the likelihood of a fall.