Bit depth refers to the color information stored into an image. High bit depth images store more color information.
Bit depth and dynamic range are often confused as one, but both are actually different yet related.
Most scanners are 30-bit color and may go up to 36, 42, or 48 bit. But a better bit depth does not necessarily mean a better dynamic range.
A 36 bit of resolution can hold numeric values necessary to represent the density range found in film transparencies.
Higher the bit depth, the more shades of black you have. This equals a higher dynamic range.