Not meant to be complete, most terms encountered by non-pro's should be
here.

Jim Warman's additions included

ABS Anti-Lock Braking System.
ACT   Air Charge Temperature (intake air, after filter).
ATX Automatic Trans.
BAP   Barometric (atmosphere) Air Pressure sensor.
BOO - brake on/off switch. see below
BPP - brake pedal position sensor.... used to be called BOO
BPS - brake pressure sensor.
CC    Cruise Control.
CCS Cruise Control Switch.
CEL Check Engine Light.
CFI   Central Fuel Inj, also called Throttle Body inj.
CPS   Camshaft (or Crankshaft) Position Sensor - used for ignition,
injection timing.
CHT - cylinder head temperature sensor.
CKP - crankshaft position sensor.
CMDTC - continuous memory diagnostic trouble code, a problem that PCM has
seen but may not be present now.
CMP - camshaft position sensor.
DPFE  Differential Pressure Feedback, Exhaust - measures EGR flow.
DSM - drivers seat module
EECIV The Engine/Trans Computer system used from mid-80's - mid 90's.
ECM   Engine control Module (before trans control > PCM).
EFI   Electronic fuel injection.
EGO   Exhaust Gas Oxygen sensor, also called O2 sensor.
EGR Exhaust Gas Recirculation (valve).- reduce emissions by lowering
combustion temperatures.
ECT   Engine Coolant Temperature sensor.
GRVPS EGR Valve Position Sensor tells ECM/PCM how far the EGR valve is
open (EGRVPS is
more commonly referred to as EVP) (Non-DPFE applications).
EOT - engine oil temperature.
EPC - electronic pressure control solenoid (inside trans).
FP    Fuel Pump.
FPM - fuel pump module.
FPR   Fuel Pressure Regulator.
FPS - fuel pressure sensor.
HEGO  Heated Exhaust Gas Oxygen sensor, heated to reach op temp earlier,
also called O2 sensor.
IAC Idle Air Control (valve).  Also referred to previously as ISC, IABP.
IAT Intake Air Temperature (sensor).
IVD - interactive vehicle dynamics.
IMRC Intake Manifold Runner Control (late model, multi-valve variable
induction).
LCM - lighting control module.
MAF Mass Air Flow (sensor).
MAP   Manifold Air Pressure sensor..used in engines without MAF
(speed-density systems)
MLP - manual lever position sensor.
MPLearn - misfire profile learn.
MTX Manual Trans.
OBDII Standardized powertrain control system from mid 90's (depend on
model)
ODDTC - on demand code - a problem that is present at the time of the
test.
OSS - output shaft speed sensor.
PCM Powertrain Control Module (engine AND trans EEC).
PCV Positive Crankcase Ventilation (valve).
PIP   Profile Ignition Pick-up - dist position pickup, ALSO the pulse
sent  TO the ECM
PPS - power steering pressure switch.
SAW - spark angle word signal.
SPOUT Spark Output, the ignition timing pulse sent back to the ignition
module based on PIP, engine RPM and sensor input.
TB Throttle Body.
TC Traction Control.
TCS - transmission control switch... also known as OCS - overdrive
cancel switch.
TFI   Thick Film Ignition - Ignition module used with EECIV, side of
dist on most models, remote on some later models.
TPS Throttle Position Sensor.
TSS - turbine shaft speed sensor.
VCT - variable cam timing solenoid.
VSM - vehicle security module.
VSS   Vehicle Speed sensor (with or instead of speedo cable).

*Test terms*:
KOEO  Key On Engine OFF, pulls memory codes
KOER  Key On Engine RUNNING, real time error info
WOT Wide Open Throttle.  Goose Test during KOER to test throttle
position sensor and engine response.
STI   Self Test input, EEC - ground to start test
STO   Self Test Output  some time same electrical lead as the CEL, but
carries the test pulse or data.