Official Tableau Knowledge Base page:
http://onlinehelp.tableau.com/current/pro/desktop/en-us/glossary.html

Visual Cues and Icons:
http://onlinehelp.tableau.com/current/pro/desktop/en-us/tips_visualcues.html

Field Types (i.e. Green vs. Blue)

Fields & Data Types:
Fields
Data Types

Harvey’s One Drive (a visual glossary):
Visual Glossary