Silkscreen (also known as legend or nomenclature) defines the text-based, human-readable information that one finds printed onto the surface of a circuit board. Silkscreen information can include component reference designators, company logos, component identifiers, switch settings, test points, other instructions, part numbers, version numbers, etc.

Generally a Printed Circuit Board (PCB) Designded by FPC supplier has many different layers and the silkscreen layer is one of these layers. Since the silkscreen must be printed on the PCB surface there are at most two silkscreen layers the top and bottom for each PCB. Silkscreens holds text information printed onto the board for humans to read and interpret.

On the silkscreen of a PCB you may print all sorts of information like the component reference designators, company logos, FPC supplier marks, warning symbols, part numbers, version numbers, date code, etc.

However space on a PCB’s surface is limited so it is best to limit it to useful or important information. Thus the silkscreen layer usually only holds a component legend showing where the various components go on the board with company logos and board design number. 

Currently custom built digtal ink- jet printers specially for priting PCBs are most often used for printing silkscreens images onto PCB surfaces from board design data. Originally silkscreens were printed using the screen printing methods from which the name silkscreen is derived. This name is due to traditional screen printing technique being known for requiring a sheet of fine cloth like silk or polyester as a screen and a frame made of wood, aluminum, etc. Now as technology advanced many different simpler or faster methods for silkscreen printing were developed but the name remained the same.