PA System Terminology 

Sound like a pro when you walk into the hire shop!

Here's a list of commonly used terms when working with PA systems.

Active Speaker A speaker that has a built in amplifier
Auxilliary Send A mixer control that allows routing of the signal to other devices.  Mostly used for sending signal to foldback speakers & effects units.
Backline Includes guitar, bass & keyboard amplifiers that musicians use on stage
Balanced Line A audio cable that has 3 wires including a shield, active signal & neutral signal. Most common example is an XLR microphone cable
Cardioid Refers heart shaped pickup pattern of a micrphone.  The popular Shure SM58 has a cardiod pattern.
Clipping Occurs when an amplifier is overloaded & cuts off the wave form. Can damage speakers.
Compressor/Limiter Limits the dynamic range of a signal.  Often used for speaker protection.
Condenser Microhone A microphone that uses an eletrical current to generate a signal (often Phantom powered)
dB or decibel A measurement of sound level.  The average person can detect a 3dB change in level.  A loud rock concert would be around 110 dB. Conversation would be around 60dB.
DI Box Stands for Direct Injection Box.   A device that allows a Line Level device such as an accoustic guitar to be connected to a microphone level cable.
Dynamic Microphone A microphone that used a Diaphragm to generate a signal.  Most vocal micrphones are Dynamic.
Effects (EFX) A device that modifies a signal.  A common example would be a reverb unit that simulates a sound being a different space.
EQ Stands for Equaliser.   A device or control that allows chaning of tone.
Fader Control on a mixer that allows control of signal level.
Feedback Often high pitched squealing noise that occurs when a microhone picks up the signal from a speaker.
Foldback Speaker Also known as a Monitor. A speaker usually placed on the stage to allow musicians to hear themselves.  Particularly for vocalists.
Front of House The main speakers
Gain A change in signal strength.
High Pass Filter A filter that only allows higher frequencies to pass.  Commonly found on mixers & used to prevent "boomy" sounds from vocals.
Impedence Electical resistance.  Speakers have a fixed impedence which is critical when attaching them to amplifiers as this affects the amount of power the amplifier can deliver.
Intelligibility Usually refers to how easy it is to understand speech through a PA system.  Often is affected by room acoustics.
Jack (or TRS) see TRS
Line Level A low level signal typically put out
Line Out A socket used for sending a signal at line level.   Commonly found on guitar amplifiers & used for connecting them to the PA via DI box.   Many line out socked have their own DI built in.
Passive Mixer An unpower mixer that requires a separate amplifier
Passive Speaker An unpowered speaker that requires a separate amplifier
PFL Stands for Pre Fade Listen.   A button on a mixer that allows one to listen to a particular channel through headphones.
Reverb An effect that simulates another space such as a hall or cathederal.   Often used on vocals.
TRS (or jack) Stands for Tip, Ring, Sleeve though generally a Tip, Sleeve connector is also called this.  This is a male plug
Unbalanced Line This up of cable has just 2 conductors, a shield & a signal cable. Often used for short cable runs between equipment & for instrument leads.
XLR A 3 pin connector that comes in both male & female types.  Used for microhone leads.