Pile:  A support which is pushed, screwed or driven into the ground, such as steel, concrete or wood.  A pushed pile (piling) is usually pushed into the ground hydraulically or mechanically using either the weight of a building or the weight of a piece of equipment (tractor) as the resistive force.  A pile driver is used to drive a pile into the ground. Pilings are more suited to nonexpansive soils, whereas piers are suited to all soil types.

 Pier:  A support which is constructed in place.  A typical pier, technically referred to as a drilled shaft pier, is constructed by drilling a hole in the ground and filling it with concrete.  Most concrete piers are reinforced with rebar (reinforcing steel). The reinforcing may be to increase the strength of the concrete, to eliminate the possibility of the pier breaking (shearing) under tensile forces, or both. 

Safety Factor:  A safety factor of 1.0 means that structure is capable of carrying no more load than the designated load.  A safety factor of 2.0 means that the structure is capable of carrying twice the designated load.  For example, if a structure weighs 5,000 lbs, if a support had a safety factor of 1.0, then it could be expected to fail if a 1 lb weight were added to the 5,000 lbs.  If a similar support had a saftey factor of 2.0, then it would not fail under a load of 10,000 lbs., but would be expected to fail at 10,001 lbs.

Pier & Beam foundation:  A foundation which is constructed on piers with a crawl space between the  floor and underlying ground. The floor is usually constructed using wood framing. There may be a concrete perimeter beam, or stem wall, which may be supported on piers or may be fully supported by the contacting soil. The stem wall is usually burried from 12" to 24" into its supporting soil.

Slab on grade foundation:  A foundation which is constructed by placing concrete directly onto the existing ground.  There is usually a water resistant membrane laid on the ground before placing the concrete.  It is usually reinforced with rebar or cables (a post-tension slab).  It can be supported on piers or it can be supported by the underlying soil.

Post tension cable slab foundation:  A foundation constructed with cables placed in the slab.  After curing, the cables are placed in tension, thus placing the concrete in a compressive state (i.e., when standard rebar is used, the compressive state of the slab is zero; when cable is used the compressive state of the slab may be 5,000 psi).  The result of the precompression is to elliminate the possibility of the concrete going into a state of tension.  

Rebar:  Steel reinforcing which is situated in the concrete to resist tensile forces. 

Concrete has a high compressive strength, and low tensile strength.  For example, a concrete with a compressive strength of 3,500 has zero tensile strength for design purposes.