Well, okay, I know what it means, but how much activity does a person need to do to be physically active? And does it have to be 'intense,' or do walking and stretching count?

lets talk about some general terms here.

Wellness is this basic idea that you're 'generally healthy' but not necessarily 'fit.' It is, in many ways, how one does the 'bare minimum' in order to prevent disease, just like taking just the RDA of vitamin C prevents scruvy, but does little else to help. For basic 'wellness' the US gov't recommends 30 minutes of activity a day--which could be walking and stretching without really exerting oneself.

For basic fitness, one needs to exert oneself. Most people agree that for basic fitness, you need at least 30 minutes of activity a day--cardio, weight training/resistance training, and stretching. Now, cardio should be 4-6 days a week, weights on 1-3 days a week, and stretching before and after each work out as a matter of 'warming up' and 'cooling down.'

For optimal fitness and health, people need to need more--and the amount that they need varies from person to person. Some people can do a great deal of activity, say 3-6 hours a day of some physical activity, 2 or more of which would be spent in some form of 'exercise'-type activity (cardio, weights, stretching). The rest of which can be spent any number of ways (walking dogs, heavy gardening, hiking, dancing, or whatever--each of these having cardio or weight training or stretching elements). Others do well with just an hour or so a day with an extended work out of 1.5 to 2 hours a day.

For me, the definition of 'physically active' is a person who is active more often than they are inactive during their waking and working hours. If they are also physically active during their working hours--cool. for me, people who tend to be moving for 2 or more hours after their work day and commute are what i consider 'physically active.'