Op amp is short for
operational amplifier, a
useful little
component in many
analog circuits. An
ideal op amp has a positive and a negative input that draw no current, and an output port that can source
CV current, where
V is equal to the voltage difference between the positive and
negative inputs, and C is a very large constant. In regular op amps, C can vary by up to 50%, but as you'll see, it doesn't matter much.
To use the op amp as an amplifier, tie the positive input to ground, and stick a resistor R1 between your input and the negative input. Then, tie the output back to the negative port with a resistor R2. The resulting amplification should be equal to -R2/R1. The best part is that R2 and R1 can usually be substituted with impedance elements like capacitors and inductors, and the equation will still hold after the appropriate Laplace Transformations have taken place.
As long as op amps are used within the spec for frequency and aren't expected to output past their source voltages, they will perform very nicely.