Ion mobility refers to the ability of ions (charged particles) to move and migrate through a substance or medium. It describes how easily and quickly ions can travel in a given environment. Think of it like the ease with which cars can move through different types of roads - some roads might be wider and smoother, allowing cars to move faster, while others might be narrower and bumpier, slowing them down. Similarly, ion mobility measures how freely ions can move in a substance, determining their speed and efficiency of transport.