AC - Air Conditioner
AE - Acceleration Enrichment
AFR - Air / Fuel Ratio
ALS – Anti-lag Strategy
ASE - After Start Enrichment

BTDC - Before Top Dead Centre

CAS – Camshaft Angle Sensor – used on some cars (mostly Japanese) to get engine position
CLT - Coolant Temperature

DRO - Digital Read-Out
DSP – Digital Signal Processing

ECU - Engine Control Unit
EGT - Exhaust Gas Temperature

GPT - General Purpose Table

HRT – Human Representation Table – all tables that convert sensor raw readings into real-life value (kPa, *C etc).

IAC - Idle Air Control
IAT - Intake Air Temperature
IGN - Ignition
IO - Input / Output
IRQ – Interrupt Requests – shows how many ‘pulses’ the processor received from the trigger sensors. Used to work out trigger sensor wiring

LTT - Long Term Trim

MAC – Motorsport Auxiliary Connector
MAP - Manifold Absolute Pressure
MBT - Minimum Best Torque/Timing - this is actually not official automotive terminology, but is a quick and easy term to signify the lowest amount of advance that produces the most torque (right at the beginning of the torque plateau in a non-knock limited engine)

NB - Narrow Band

OEM - Original Equipment Manufacturer

PID -  Proportional Integral Derivative
PnP - Plug n Play

PW – Pulse-Width – mainly relating to injection pulses
PWM - Pulse Width Modulation

RAW – Raw reading from the ADC sensors (0-65535). In newer MEITE versions this is convertible into Volts and Ohms (for temperature sensors)
RPM - Revolutions Per Minute
RTI - Return To Idle

TDC - Top Dead Centre
TPS - Throttle Position Sensor

VE - Volumetric Efficiency
VSS – Vehicle Speed Sensor
VVT - Variable Valve Timing

WB - Wide Band
WBO2 - Wide Band O2 Sensor
WOT - Wide Open Throttle