Piles are deep foundations used to transfer structural loads through weak soil layers to stronger soil strata below. There are different types of piles based on function (load bearing, non-load bearing), material (concrete, timber, steel), and installation method (driven, cast-in-place). Load bearing piles can be end bearing piles that rest on a hard layer or friction piles that transfer load through side friction. Factors like soil conditions, water table, and cost determine the suitable pile type for a given foundation. Load capacity is estimated through testing, soil parameters, or dynamic/static formulas.