Nexus Help. Reflexes are what Nexus collectively calls all of its scripting and automation elements.
When you create an alias and a trigger, and maybe use a variable or two, you're creating a set of reflexes. They are generally intended to make your life easier by performing some mundane maintenance task or by creating a fast-paced twitchy combat system to more easily defeat foes one-on-one. Variables are probably the simplest type of reflex. Aetolia, the Midnight Age.