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.
We pride Ignition on being UNlimited, but sometimes you want a smaller system at a lower cost. The "limited version" of Ignition refers to using a special license that applies restrictions to some or all of the Ignition modules. See the modules section for more information, and ask your sales representative for information about pricing.