WordNet
n. the layer of epidermis immediately under the stratum corneum in the skin of the palms and soles
Wikipedia
The stratum lucidum (Latin for "clear layer") is a thin, clear layer of dead skin cells in the epidermis named for its translucent appearance under a microscope. It is readily visible by light microscopy only in areas of thick skin, which are found on the palms of the hands and the soles of the feet.
Located between the stratum granulosum and stratum corneum layers, it is composed of three to five layers of dead, flattened keratinocytes. The keratinocytes of the stratum lucidum do not feature distinct boundaries and are filled with eleidin, an intermediate form of keratin.
The thickness of the lucidum is controlled by the rate of mitosis (division) of the epidermal cells. In addition, melanosomes determine the darkness of the stratum lucidum. The cells of the stratum lucidum are flattened. They are surrounded by an oily substance that is the result of the exocytosis of lamellar bodies accumulated while the keratinocytes are moving through the stratum spinosum and stratum granulosum.