Exercise vs. Activity?! Are these not the same thing? No, not quite.
Exercise is strenuous or “formal” exercise that gets you sweating and out of breath (you can talk but not sing). Examples include running, very brisk walking, cycling, fast swimming, most gym exercises, weight training, aerobics classes, and most team sports.
Activity is gentler or “incidental” activities that are not a strain as such but do involve movement and action. Examples include walking, shopping, gardening, housework, gentle swimming (good swimmers), DIY handiwork, and most yoga classes.
You can perhaps see that there is some overlap between these (for example, very busy and “rushed” gardening can become quite strenuous, yoga can be strenuous, DIY can be both strenuous and stressful for some, and some people are pretty relaxed even at gyms) but the general idea is the important thing.
You need both of these. They give different benefits and it is important to exercise AND to be active. Most experts suggest that we try to do 150-180 minutes of exercise a week and 30 minutes of activity every day. There is much more detail that you can learn about but this is a good place to start.