Opamps have a very high intrinsic gain, something in the order of 150,000 and higher; this is called the open loop gain. This gain is not very useful by itself since it is very unstable; it changes with temperature, supply voltage and also requires extremely small signals to work within a useful range of voltages without clipping the incoming signal.
A method deviced from the conception of the opamp is the use of a feedback loop to limit the gain of the op amp to lower than 100, but that the gain will only depend on external components instead of the built in properties of the device.
The feedback is connected in a way such that any increase in the feedback signal will lower the output, similar to adding a negative, hence it's name.
