Original: The unit symbol "KB" is a commonly used abbreviation for "kilobyte" but is often confused with the use of "kb" to mean "kilobit".
Simplified: For example, "MB" means "Megabyte" and "Mb" means "Megabit". It's easy to confuse the two, but bits are much smaller than bytes, so a lowercase "b" should be used when referring to "bits" and an uppercase "B" when referring to "bytes".