Obesity
Obesity is when a person's body stores much more fat than it needs to stay healthy.
Think of it this way
A pantry shelf holds jars of cooking oil, some jars for today's meals, a few jars stored for later. In obesity, the body keeps adding oil jars to the shelf long after the space is full. The jars stack up in rows and layers, crowding out room for other things. The shelf holds far more stored oil than the body will ever use.
Explaining obesity by grade level
Your body needs some fat to stay warm and have fuel. But too much fat can make it hard to move and play. Sitting still for a long time means the body does not burn its fuel. That is why being active helps keep the right amount of fat.