Last updated at 12:20 am UTC on 19 April 2017
The usual meaning of "Smalltalk" is either the Squeak programming language or the historical programming environment that Squeak derives from. Note that the "t" in Smalltalk isn't capitalized.
Squeak is a descendent of Smalltalk-80. The core developers of Squeak (then named Squeak Central) in fact included many of the core developers of Smalltalk-80.
Squeak's language and much of the class library is identical to that of Smalltalk-80: they both have objects, classes, single inheritance, blocks, garbage collections, collections, streams, model-view-controller, and many other bits. In the meantime the class liberary has been extended considerably.
ANSI Smalltalk is a recognized standard for Smalltalk. While Squeak is Smalltalk in spirit, it is not fully compliant with the ANSI Smalltalk standard. There is temporarily an add-on on SqueakMap which tries to move Squeak towards ANSI compatibility.
Also see: Smalltalk overview Squeak's programming language Squeak websites Smalltalk & Squeak books Camp Smalltalk Improving Smalltalk
Smalltalk is as well a global variable.
After the environments changes in March 2017 (Squeak 6.0alpha) references to it have to be replaced.
More see Smalltalk global variable