A system is any process, policy, or procedure that consistently achieves the same result, regardless of who is completing the task.
Clear systems will free you from the day-to-day functioning of your organization. Your company will run more smoothly, turn a higher profit, and provide a higher level of service - regardless of your involvement.
Any task that is performed in your business more than once can be systemized. Ideally, the tasks that are completed on a cyclical basis - daily, weekly, monthly, and quarterly - should be systemized so much so that anyone can perform them.
Systems can take many forms - from manuals and instruction sheets, to signs, banners, and audio or video recordings. They don't have to be elaborate or extensive, just provide enough information in step-by-step form to guide the person performing the task.
Systemizing your business is also a healthy way to plan for the future. You're not going to be working forever - what happens when you retire? How will you transition your business to new ownership or management? How will you take that vacation you've been dreaming of?
Businesses that function without their ownership are also highly valuable to investors. Systemizing your business can position it in a favorable light for purchase, and merit a high price tag.