Bit

The Bit is an item added in the 23w13a_or_b snapshot. Its icon is entirely black as if it's a single black pixel. It can be used to craft some of the Tags.

In survival, put a Name Tag into a Stonecutter to cut it into either 16 "Name" or 16 "Tag" items. These can be cut further into 16 Bits each. For an unknown reason these are the only two that can be cut into bits.