You can leave the key under the door mat (=one by a door to clean your feet on).
►a table/place mat
(=one that you put under a dish to protect the table)
1 a small piece of thick rough material that covers part of a floor: The men knelt on their prayer mats. You can leave the key under the door mat (=one by a door to clean your feet on).2a small flat piece of wood, cloth, etc. that protects a surface, especially on a table: a computer mouse mata table/place mat (=one that you put under a dish to protect the table)3a piece of rubber, used for exercise, or for falling down on in some indoor sports: an exercise mat a gymnastics mat4a piece of thick paper that is put around a picture inside a frame5a mat of hair/fur/grass etc. a thick mass of pieces of hair, fur, etc. that are stuck together → see alsomatting