The word truffle, as it applies to a chocolate confection, traditionally refers to confections that look like the truffles (fungus) dug from the ground - irregularly shaped and very often covered with cocoa powder. Traditional truffle centers are made by hand-rolling usually fairly dense ganaches (high chocolate to liquid ratio) and not worrying at all about whether they are perfectly regularly shaped. Traditional truffles are sometimes referred to astruffe nature or natural truffle because of that resemblance.
Depending on how long the truffle needed to last (and the maker's thoughts about texture), a truffle may be covered (mechanically enrobed or hand dipped) with chocolate. Further embellishment may come in the form of additions or alternatives to the cocoa powder coating - green tea powder is common in Japan, shredded coconut, and nuts in one form or another are also common; any these may be used with or without the chocolate covering.
The hand formed truffle is contrasted with two other production methods:
A) Slabbed (usually ganache, but may be layered with pate de fruit, caramel, or other element) pieces that are then enrobed and may be further decorated. A slabbed ganache that is covered in a powder or left uncovered is sometimes called a pav (maybe referring to the gem cut, or to a paving stone).
B) Shell-molded pieces.
The important technical difference between slabbed and shell-molded pieces is that in a slabbed piece the center forms the support for the chocolate shell; in a shell-molded piece, the shell forms the container for the center, which tends to be softer than that of a slabbed piece.
I use the word bonbon (from the French, colloquially "good good") to refer to slabbed and shell molded pieces. I don't use the word praline (which I believe is Belgian in origin - as contrasted withpralin, which refers to caramelized nuts and is French) because it is already so overloaded with meanings. I use truffle to refer to a truffe nature.
Bonbon, praline, and truffle have all been conflated over time and are generally used interchangeably though technically, at least in my mind, they refer to different final forms based on the method of production.
PS. I useFrench (aka southern European), Belgian (aka northern European), American, and Nouvelle American (or nouveau French) to refer to different generalized approaches to flavor in ganaches and centers, not to physical styles of work.
clay - http://www.thechocolatelife.com/clay/