Mobility includes all of our joints and the muscles, tendons, and ligaments that control and move them. Some people have total mobility meaning that they enjoy freedom of movement in all of their joints and that they do not suffer from arthritis or any other type of inflammation on a regular basis. They haven't had any consequential joint or muscle injuries or diseases, or broken bones, over the course of their life and enjoy relatively good health.
Others have more limited mobility in certain joints or need to rely on the assistance of a walker, cane, crutches, or wheelchair to get about in their home. Some just steady themselves with walls or furniture as they move about in their homes. Some have essentially no mobility in the sense that we normally think of it because they are confined to a bed or have severe limitations in the use of their limbs.
So far, this is treating mobility in the classic sense - the way that people generally regard it. However, mobility is so much more than just moving about in one's space or in the world outside their homes.
Mobility affects us in most everything we do. We can't drive a car for instance without being about to open the car door (and then close it after we are seated), sit down behind the wheel, adjust the mirrors, turn our head to look behind us and to the side, move our head and our eyes to look at those mirrors and our gauges (including the speedometer), start the engine, put the car in gear, step on the gas (accelerator) and then the brake (the clutch also if it's a manual transmission), open the windows, and play the stereo.
Making coffee in the morning requires turning on the faucet and filling the pot with water (or using bottled water) as we hold it and keep from dropping it (unless our coffee maker is plumbed to provide the necessary water for this task), getting the coffee canister and opening it, measuring out the proper number of scoops of coffee, placing a filter in the basket, putting the carafe in place, and turning on the system.
Preparing a meal or even a sandwich requires a similar array of steps and abilities. Plus, we have to open drawer or cabinet doors, retrieve cooking vessels and utensils, possibly open the refrigerator, open the microwave or oven door (or turn on the cooktop), set the time or the temperature, and stir or manage the contents of what is being cooked or prepared. We may have to open jars or packages, or slice meat or vegetables also. We may need to turn on the faucet to wash or rinse what we are preparing and to wash our hands.
Standing, sitting, squatting, kneeling, bending, lifting, reaching, grabbing or grasping, holding, opening boxes, and twisting the lids off bottles or jars are all functions of mobility that we likely don't think of in these terms.
There are so many other things we do in the home that concern mobility so let's keep a very broad mind as to just what constitutes someone's need to function well in their space regardless of any limitations they may have.