This stands for "Web Download." It means the file was losslessly ripped from a streaming service (like Amazon or iTunes), generally providing better quality than a "WebRip."
For technical discussions or release notes, community forums like Blu-ray.com often have threads dedicated to various digital and physical releases. This stands for "Web Download
When a series of mysterious, hallucinatory "suicides" plagues London, young Sherlock Holmes and his new friend John Watson investigate a sinister religious cult. hallucinatory "suicides" plagues London