What is microphone frequency response? Is it basically the sound level of your voice that the microphone can pick up?
The frequency response of a microphone transducer (either a microphone or a speaker) is the range of frequencies that the device is capable of accurately sampling or reproducing.
In more technical terms, audio transducers act as bandpass filters. This means that they have both a lower corner frequency, and an upper corner frequency. The gain at each corner frequency is -3dB with respect to the peak gain which is typically right in the middle. Nominal gain for accurate sampling and reproduction is 0dB, anything smaller is attenuated and anything larger is amplified.
The range of human hearing for most adults is between 20hz and 20,000Hz. Children can typically hear higher frequencies, up to about 24Khz.
High quality surround headphones will often add a subwoofer into each earpiece. The subwoofer may have corner frequencies of 20hz and 200hz, which when coupled with one or more additional acoustic transducers that have a range of 100hz through 20,000hz provides a fairly flat response from 20hz through 20Khz provided that the output signal is passed to the device best capable of handling it. If you've ever played with a surround sound system, you may have seen a setting called "bass crossover frequency", that is what this is for. Professional surround sound speakers will often have three or more acoustic transducers per speaker to ensure accurate reproduction of all frequency components in the human hearing range.
Communication microphones rarely have more than one microphone transducer in them, as the frequency range of human speech is much more narrow than the frequency range of human hearing. However, professional microphones that are designed to pick up all audio will have a range that is much wider. If you are simply buying a microphone for gaming, a range <5Khz is fine.