Wiegand comes from the term Wiegand Effect which is a magnetic effect or field that is created when a keycard carrying these wires is placed within proximity of a similar magnetic field reader.  The code is embedded within the card and is read through the presence or absence of these Wiegand wires.

Wiegand is the most common communication standard for proximity cards around today.  Most cards and readers are defined using these standards, and range in bit length.  Bit length is defined as the distance the data travels on a card to determine its device code and facility code.  Longer bit lengths allow for more facility codes and device codes to be created.  The most common is 26 bit length which has facility codes ranging from 0-255 and device codes ranging from 0-65535.