AM -- Amplitude Modulation

Frequency - Frequency of AM Broadcast Station--in US, 540 kilohertz to 1700 kilohertz

ND (Omnidirectional) - In theory, a circular pattern that transmits equally in all directions.

Single tower (1 tower) - always a ND or Omni-directional station.

Directional - An AM station that uses two or more station and transmits something other than an Omni-directional signal.

Maximums-  Refers to a directional broadcast station where the maximum signal is transmitted in a given direction.

Nulls-- Refers to a directional broadcast station where the minimum signal is transmitters in a given direction.

Monitor Points-  Refers to a location specified on an AM broadcast license, normally in station nulls, with a maximum
                          specified signal level given in mV/m.  They are used to determine if a broadcast stations directional
                          antenna pattern is operating as licensed.

Daytime - Refers to time between local sunrise and local sunset.  On station licensed, is given in non-advanced time      
                and changes monthly.

Critical hours - a period between two hours prior to local sunset.

Nighttime -  Time between local sunset and sunrise.  Also non-advanced time and changes monthly.

Two-site operation - Indicated on an AM broadcast license and refers to a station that operates from different sites for its
                               daytime and nighttime operation.

Daytime only -- A station that only broadcasts during daytime hours and must sign off the air at local sunset.