Proprioception is a term used when talking about balance. It is the ability to interpret and use information about your position in space. Through a complex system of environmental feedback, cues from the bottom of your feet, the relation of you inner ear to gravity, and what you see, your body senses which muscles to activate or deactivate to maintain your desired position. It does this when you stand, get up from a chair, or walk on the sidewalk. It also uses all of these cues when you're riding your bike, skiing, strength training at the gym, and standing on you tiptoes to grab something from the top shelf. When the information received is too complex to translate, the system gets overwhelmed and you lose your balance. With practice and experience (i.e. balance training) you can master what once seemed like impossible tasks. (IDEA Health & Fitness Association)
Here are a few examples of some tools and exercises you can to increase your balance.