Cume Persons:  the total number of DIFFERENT persons listening to a radio station per week. This reflects the total number of people who tune in to a station for at least five minutes throughout the week.  Each person is only counted once.

Average Quarter Hour Persons: the average number of people listening to a radio station at any given time. This can best be explained by saying "this represents the average number of people who will hear your commercial each time it runs".

Frequency: the average number of times a station's heavy listeners will hear your message. The magic number you want here is at least 3.29 times. (See "The Perfect Schedule" for more details.)

Time Spent Listening:  the amount of time listeners spend with a given station.  This is crucial in determining how many commercials are necessary to achieve the greatest impact for your campaign (see The Perfect Schedule).