Definition
A black triangle containing a white letter 'T' printed on an instrument approach chart or in the Chart Supplement to indicate that the airport has non-standard takeoff minimums and/or non-standard departure procedures. The symbol directs the pilot to consult the Takeoff Minimums and (Obstacle) Departure Procedures section of the Terminal Procedures Publication for that airport before departing under instrument flight rules.
Plain English
A small symbol -- a black triangle with a 'T' inside -- that flags an airport as having special takeoff rules or departure paths. When you see it, you have to look up the airport's takeoff page before you fly out under IFR.
Context Anchor
Seen on FAA instrument approach charts and in takeoff minimums sections before planning or flying an IFR departure.
Derivation
The 'T' simply stands for 'Takeoff.' The triangle is a standardized FAA chart symbol used to draw the eye to a flag or warning -- the same way the 'A' in a triangle marks special alternate minimums.
Why Pilots Care
Alerts pilots to check for higher visibility or ceiling requirements and any required departure routing to clear obstacles safely.
Intuition Check
The triangle T is not decoration and it is not the takeoff minimum itself. It is a pointer telling you to check the separate published takeoff and departure information.
Example Sentence 1
During flight planning, the pilot noticed the triangle T on the approach chart and pulled up the takeoff minimums page to check for any obstacle departure procedure.
Example Sentence 2
Because of the triangle T on the plate, we used the published obstacle departure procedure instead of a visual climb.