Actuator - electro-mechanical device which converts analog or digital electrical inputs into mechanical energy interacting with the physical world.
ADC - Analog to Digital Converter, encodes analog signals into digital values.
API - Application Programmerís Interface, provides function call interface to lower level software and/or hardware functionality.
Application Executive - Also known as a Cyclic Executive, a main loop program that calls functions on a periodic sub-rate of the main loop period.
Asynchronous - An event or stimulus that occurs at any point in time rather than at known predictable points in time - e.g. an external interrupt may occur at any time and will immediately change the thread of execution on a CPU.
Asynchronous Logic - Digital logic that is not globally clocked, but rather changes state based on edge triggering in a combinational logic circuit or edge triggered by multiple independent clocks.
Atomic Operation - A non-interruptable CPU instruction - i.e any instruction that can be fetched and completed before the CPU can be interrupted.