what does % do in lua code example

Example: What is lua used for

Lua is a powerful and fast programming language that is easy to 
learn and use and to embed into your application. 

Lua is designed to be a lightweight embeddable scripting language.
It is used for all sorts of applications, 
from games to web applications and image processing.

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Used commonly in Roblox, Garry's Mod and Multi Theft Auto