A short word you put in front of a list when you are about to name the exact things you only hinted at a moment before. You write something general — "three of the founding members", "the usual charges" — and then you write viz, and then you say who or what you actually mean. It is short for the Latin videlicet, meaning "it is permitted to see", i.e. "namely". Almost nobody says it out loud; when people do read it aloud, they usually say "namely" instead of the letters. It belongs to written English of a formal, old-fashioned, slightly legal kind — contracts, minutes of meetings, academic footnotes, older textbooks. In ordinary writing today, people write namely, or that is, or just a colon. Two things worth knowing. First, viz introduces the FULL list of what you meant — everything, not a sample. If you only want to give an example or two, you want e.g., not viz. Second, viz is not the same as i.e.: i.e. rewords one thing in different words, while viz names the members of something you described as a group. The comma after it is optional and older writers often left it out. You are far more likely to need to READ this word than to write it — if you are writing, namely will serve you better and no one will think less of you.