This is a 5V 2-Channel Relay module, it allows the Arduino to control high power sources (see ratings below).

• 2 Relays on board
• Normally Open (NO) or Normally Closed (NC) operation
• Each 5V Relay requires 20mA driving current
• Each relay is activated by an ACTIVE LOW signal (0v).
  
• 5V 5mA TTL control input which can be directly controlled by Arduino, AVR, PIC, ARM and others.
• Indication LED for each Relay's Status
• Relays are rated at 10A@250VAC and 10A@30VDC
• Dimensions 4.5cm x 5cm