Definition
An ATC instruction directing the pilot to switch the transponder to either the LO (low-sensitivity) or NORM (normal-sensitivity) power setting. NORM is the standard operating position used for the vast majority of flight; LO reduces transponder reply power and is used only when ATC specifically requests it, typically to resolve interference or overlapping returns when an aircraft is very close to the radar antenna.
Plain English
ATC is telling you to set your transponder to either its normal power setting or its low-power setting. Normal is the everyday setting; low is rare and only used when ATC asks for it.
Context Anchor
Heard in radio communication with air traffic control when a controller needs a specific transponder setting for radar identification or radar display quality.
Derivation
"Squawk" entered aviation use during World War II from the IFF (Identification Friend or Foe) system codenamed "Parrot" -- pilots were told to make their transponder "squawk" like a parrot. "Low" and "Normal" describe the transponder's reply power output.
Why Pilots Care
Using the correct setting keeps your aircraft visible to controllers while avoiding unnecessary replies that could clutter radar in high-traffic areas.
Intuition Check
Do not read “Low” as flying low or speaking more quietly on the radio. Here it means the transponder’s sensitivity setting. Do not read “squawk” as a voice transmission. Here it means operate the transponder as instructed.
Example Sentence 1
Cessna 12345, squawk normal -- the controller's request to return the transponder to its standard power setting.
Example Sentence 2
Once we were clear of the pattern, approach instructed us to squawk normal for full radar coverage.