What's the difference?
Weight lifting is strength training, using dumbbells, barbells, or whatever you lift that makes your muscles work harder than to what they are accustomed.
Weight bearing exercise is usually considered cardiovascular exercise done on your feet, such as walking, jogging, stepping, dancing, cross-country skiing, elliptical exercise machines, hiking, or aerobic workouts. This type of cardio can help maintain bone mass over the years, if it is done consistently.
Lifetime walkers can have higher bone mineral densities than those who don't walk on a regular basis. Walking needs to be brisk in order to make a difference in your bone density and your fitness. One important point to remember: Research shows that walking doesn't do nearly as much as strength training for building bone, so keep strength training 2 to 3 times a week, on non-consecutive days. No matter if you have great bone density now, you need to strength train to keep those bones strong over the years!