Multistation access unit is a central equipment which is used in Token ring topology. All the devices are physically attached to the device in star topology fashion but internally the devices communicate on token by token basis in ring form. The MAU generates token which is ciruclated to each connecting end device, After the token is free or the timestamp of that token has finished, it is assigned to very next device in ring chain.
Timestamp is a value assigned by any device which keeps records of time & date, very useful in troubleshooting.
Token ring topology with MAU is obsolete and not used anywhere now a days.