Self Regulation refers to our ability to direct our behavior and control our impulses so that we meet certain standards, achieve certain goals, or reach certain ideals. Self regulation involves being able to set goals, monitoring one's behavior to ensure that it is in line with those goals, and having the willpower to persist until goals are reached.
One example of a situation that requires self regulation is when you go on a diet with a goal of losing X number of pounds. In order to be successful, you must stick to a diet and exercise plan, at least until you reach your target weight. This means being able to say no to certain foods that are not part of your meal plan, getting yourself to eat certain food that you might not like very much, being able to motivate yourself to get up and do your daily workout, and other things that are needed to achieve your goal. In this case, good self-regulation may spell the difference between achieving your ideal weight and being healthy, or spiralling out of control into obesity and ill health.