GPS is global positioning system. With satellites the position on earth is calculated.
To calculate the exact position you need GPS hardware. GPS hardware exist of many different things. You have GPS antennas, GPS receivers and GPS modules. They all have their purposes.
These antennas receive the signals that the satellites send to earth. The more signals are received the more accurate the position can be determined.
GPS modules are the brains for determining the position. In these modules all the calculation is done. All satellite signals are combined to determine one exact position.
A GPS receiver is an object where a GPS antenna and a GPS module are both integrated. With a receiver you can determine the exact position.