Lock makes sense to me, even if I don't think it is the best description. There are two water levels, high and low side of the lock. The lock smoothly transit

Lock makes sense to me, even if I don't think it is the best description. There are two water levels, high and low side of the lock. The lock smoothly transitions you from one level to the other. A media query without the transition would be like navigating a boat down a waterfall rather than down a lock; jarring!