Local Area Network. Refers to internal networks contained within an enterprise as opposed to WAN (Wide Area Network) which joins LANs into "super" LANs (such as combining three different locations each with their own LAN). This is often referred to as Intranet (not Internet). Intranet can include many LANs connected into a WAN for a single company.
A 6 digit key that (when loaded) contains information about the Ignition Gateway and it's modules. You can run an unlicensed Ignition in Trial mode, or you can load a license and have unlimited access to the modules. You can also install modules that are not on the key, and they will run in trial mode.
In Ignition we refer to libraries in several places, but it just means a collection of similar items. These could be a collection of images, scripting functions, components, or more.
We often talk about layers in Ignition in reference to the software stack. Each layer is a piece that works because of the layers below it. For example, the Platform layer of Ignition requires the VM (Java) layer below it to function, and is required by the Module layer above it.