"X-Ray resource pack" typically refers to a type of Minecraft texture pack that makes common blocks (like stone, dirt, and gravel) transparent or semi-transparent while keeping high-value blocks (like ores, chests, and spawners) opaque.
These are actual code modifications. They allow you to "search" for specific blocks and can often see through solid chunks more effectively than a texture pack. The "Rules of the Road": Ethical Use
One common myth is that X‑ray texture packs are “undetectable” because the server doesn’t know what texture pack you’re using. While technically true, servers can still monitor your behaviour—such as mining directly to the richest ore veins without any exploratory tunnelling—and flag you for cheating.