Humans are sensitive to a particular range of frequencies, typically from 20 Hz to 20000 Hz. Whether you can hear a sound also depends on its intensity - we're most senstive to sounds of a couple of thousand Hz, and considerably less sensitive at the extremes of our frequency range.

We generally lose the top end of our range as we age.

Other animals are sensitive to sounds at lower or higher frequencies. Anything less than the 20 Hz that marks the lower range of human hearing is classified as infrasound - elephants, for instance, communicate using low frequency sounds. Anything higher than 20 kHz, our upper limit, is known as ultrasound. Dogs, bats, dolphins, and other animals can hear sounds in this range.