Viz. is an abbreviation used sort of like i.e. or e.g., but less frequently and with the purpose of elaborating on something expressed before. For example, you could say I study linguistics, viz. etymology and conlanging. The term was originally Tironian shorthand for the Latin word videlicet, which basically translates to "namely" or "that is to say". Interestingly enough, videlicet is actually a contraction itself, combining the words videre and licet, which meant "to see" and "allowed", respectively (so, together, videlicet means "it is allowed to see"). Videre, through Proto-Italic wideo, derives from the Proto-Indo-European word weyd, still with the same definition, and licet is thought to trace to Proto-Indo-European leyk, which would mean "to prepare for sale" (it was associated with auctions).
Adam Aleksic, a rising sophomore studying linguistics and government at Harvard University, has been described as the internet's sixth most famous etymologist. He also has disturbing interests in politics, vexillology, geography, board games, conlanging, and law.