Acronyms - There are so many acronyms in electronics... here is a good site to look up acronyms http://www.acronymfinder.com/

AWG—American Wire Gauge formerly known as the Brown and Sharpe (B + S) Gauge. The gauge is calculated so that the next largest diameter always has a cross-sectional area that is 26% greater.

ASTM—American Society of Testing and Materials.

Access Hole, Inner Pad - A series of larger diameter holes in successive upper layers of a multilayer printed circuit board such that each of the holes has its center on the same central axis and the main hole in the board. These open relief areas provide access to the surface of the internal copper land on an inner layer of the pc board for testing or attachment. Sometimes used to insulate the bottom pad of a board from a conductive mounting surface.
 

AC or Alternating Current
There are two types of electrical currents in electronics, Direct Current and Alternating Current. AC and DC are descriptive labels referring to the electron flow patterns in a conductor verses time. First the flow may be positive in voltage then it changes to negative voltage causing current to flow in alternating directions in the conductor. Direct current is typically a steady state voltage that mimics the pattern seen when a battery cell is attached to a complete circuit with current flowing in only one direction. AC is an alternating current that varies with time allowing the electron current to flow in both directions along the conductor at a fixed or variable rate,  switching polarity many times per second. Some common types of waveforms associated with alternating currents when viewed using an oscilloscope will take the shape of a sinusoidal, square wave , or triangular and saw tooth wave pattern.

Square Wave

Approximating the square wave

Sine wave

Triangular wave

Saw tooth wave

Ambient
Typically the average air temperature surrounding the heat source or system that must have a path for component heat flow to cool the unit under test. Under electronic test conditions the ambient temperature that the unit may be exposed to must be artificially raised and lowered to the maximum temperatures that the unit under test would be exposed to in normal use.

Anchoring Spur
An extension of a land on a flexible printed board that extends beneath the cover lay to assist in holding the land to the base material typically used for Flex Circuits between the layers of Kapton to reinforce the pad structure.