What characteristics of a sound wave allow you to

Explain what characteristics of a sound wave allow you to be able to distinguish between a car horn and the trumpeting sound of an elephant.
What characteristic of a sound wave determines its loudness?

the frequency is what allows you to distinguish between different sounds, spork284 is correct.

You guys are right.
The variations in the sound waves are referred to as harmonics.

There are various parts to what makes certain sounds. Most sounds are defined by pitch, loudness, and timbre.

Pitch is usually the main frequency you hear. If you hit a tuning fork it would generate a certain frequency, that could be characterized by a sine wave. Not all sounds though are made up of individual sine waves, but combinations of them. If you were to do a Fourier Transform of the signal from a certain sound (look at the size of the signal with respect to frequency, rather than time), you would find that it was made up of various frequencies with varying amplitudes.

So if you play the 'C' note on the Piano, and then play the 'C' note on a Saxophone, it is the same pitch, or total frequency, but the individual frequencies that are added to make the whole sound will vary in frequency and amplitude.