HLDS: The "High Level Data Structure".  See hlds.nl.

moduleinfo: Another name for the HLDS.

LLDS: The "Low Level Data Structure".  See llds.nl.

inst: instantiatedness.  Indicates whether a variable is free, partially
      bound, or ground.

mode: this has two meanings:
	(1) a mapping from one instantiatedness to another
		(the mode of a single variable)
	(2) a mapping from an initial instantiatedness of a predicate's
		arguments to their final instantiatedness
		(the mode of a predicate)
	
proc (procedure): a particular mode of a predicate.

procinfo: the structure in HLDS which contains
	information about a procedure.

predinfo: the structure in HLDS which contains information about
	a predicate.

globalinfo: a structure used by codegen.nl

codeinfo: a structure used by codegen.nl

switch: a disjunction which does a case analysis on the toplevel
	functor of some variable.