UHD stands for "Ultra High Density" and provides the most compact connector layout or footprint on the adapter panel. UHD enclosures or panels can only accept UHD adpater panels or cassettes.

SHD stands for "Super High Density" and provides a more compact connector layout or footprint on the adapter panel. SHD chassis enclosures can only accept SHD adapter panels or MTP/MPO cassettes.

The amount of fiber strands that you can fit into an enclosure will depend on how many panels or adapters you can fit and what type of connectors you choose. For example, if you choose a 1 panel enclosure and use a 12LC adapter panel, you can house or couple 12 fibers in that enclosure. If you use 12 MTP/MPO adapter panel, you can house or couple 144 or 288 strands depending on whether the MTP or MPO connector being connected is a 12 or 24 fiber connector.

LGX stands for Lucent Connector Group and is often called Lucent Global X. It was originally Lucent Technologies standard for fiber optic adapter plates and enclosures but over time it became industry standard.

The three main chassis are LGX, SHD, and UHD. LGX is the most common and standardized chassis type.