HP L43766-001 is a 16 GB memory module for systems that use compatible desktop DIMM memory. Its DDR4 format and ECC support make it a defined memory option for a compatible system.
The module is DDR4-2666, also listed as 2666 MHz and PC4-21300. It is an unbuffered, 288-pin DIMM with error checking and correction (ECC), so its memory type and form factor are clearly specified for system matching.
This is a single 16 GB memory module. The listing does not specify additional package contents.