A mug is a dish for holding a warm drink. A mug of your favorite warm drink can be very comforting.
Some mugs are better insulated than others and will keep drinks hot or cold for a longer time. Some mugs are designed for travel. They have lids, so it is less likely that the liquid they contain will spill during a commute or other trip. The lids usually have a slot or small hole, so you can drink without removing the lid.
Most mugs have a handle, but some insulated travel mugs do not.