To setup Wireless Serial Communication, HC-05 Bluetooth Module is most demanding and popular due to its low price and extremely high features.
This module can be used in Master or Slave Mode and easy switchable between these two modes, By default Slave mode is configured.
Modes can be changed using AT Commands.
The slave mode in HC-05 cannot initiate a connection to another Bluetooth device, but can accept connections.Master mode can initiate a connection to other devices.

HC-05 Specifications:- 
Profiles: Bluetooth serial port Profile
Bluetooth protocol: Bluetooth Specification v2.0+EDR
Frequency: 2.4GHz ISM band
Modulation: GFSK(Gaussian Frequency Shift Keying)
Emission power: ≤4dBm, Class 2
Sensitivity: ≤-84dBm at 0.1% BER
Speed: Asynchronous: 2.1Mbps(Max) / 160 kbps, Synchronous: 1Mbps/1Mbps
Security: Authentication and encryption
Power supply: +3.3VDC 50mA
Working temperature: -20 ~ +75Centigrade
Dimension: 26.9mm x 13mm x 2.2 mm

HC-05 Applications:-
Embedded Projects
Industrial Applications
Computer and portable Devices
GPS receiver