This is the official North American Scrabble Lexicon.

TWL was previously know as OSPD (Official Scrabble Players Dictionary). The general public typically treats OSPD and TWL as the same.

OSW - "Official Scrabble Words"

This was the UK's official lexicon until this year, when the UK switched over to SOWPODS.

SOWPODS - "Official Scrabble Words + Official Scrabble Players Dictionary"

Combination of the OSW and OSPD (now TWL) dictionaries. This is the lexicon used by the majority of International countries. Most world tournaments are played using this dictionary.

JGOSW - "SOWPODS - TWL"

The SOWPODS dictionary with TWL removed. This is provided merely as a study tool for North American players that occasionally play in International SOWPODS tournaments. It is used to help keep the OSW only words mentally separated from TWL words. This dictionary concept was created by Jim Geary (thus the name JGOSW).