From Longman Dictionary of Contemporary Englishmouse matˈmouse mat (also mouse pad American English) noun [countable] 
a small piece of flat material with a special surface which you move a computer mouse on
a small piece of flat material with a special surface which you move a computer mouse onExamples from the Corpus
mouse mat• Furthermore, the pen is more compact and requires no mouse mat.From Longman Business Dictionarymouse matˈmouse mat British English, mouse pad American English noun [countable]COMPUTING the thing on which you place a computer’s mouse, and which allows you to move it easily 