This is a 4x4 keypad matrix shield i.e it have 16 switches arranged in 4 rows and 4 columns numbered from 0 to F. There are 8 male burg strips for 16 pins that mean 8 pins configuring 16 signals. This is possible with the help of multiplexing technique. Underneath each key is a pushbutton, with one end connected to one row and other end connected to one column. So whenever we press any key then its corresponding row and column pins gets multiplexed and gives a muxed output at one of the 8 male burg strips. This Keypad Matrix Shield is comfortable with microcontroller boards like 8051, Arduino, PIC, AVR, ARM etc. Male burg strips corresponds to rows and columns. These pins can be output or input for the microcontroller depends on projects. Push button for every number. A single push button directly connected to one row and one column.