AVR ISP cable with USB interface. ISP=In System Programming.
When printer port is available (as on most desktop PC-s), a cheaper alternative is a 5-wire dummy DSUB25 => pinheader "stk200" cable (or "bsd" cable see avrdude config file). But new notebooks don't have printer port, only USB.
This was used with atmega168 and atmega128 and seems to be compatible with the atmega AVR risc microcontrollers. Related pinouts
Most users do NOT need this, see the USB-RS232 cable for normal operation for vemstune