Timbre

Timbre and tone are closely related, but not usually thought of as the same thing. When using the word "tone", we're usually referring to a specific instrument and/or player. "Timbre" (which is italicized because it's taken from the French) usually refers to the characteristic sound of a family of instruments, and then further to individual members of a particular family. 

There are the strings, which can be bowed orchestral instruments or guitar, banjos, and mandolins and such which are plucked or strummed. There are the brass instruments, some of which have conical tubing and others with cylindrical tubing. There are the single reeds - the clarinets and the saxophones - and the double reeds - the oboe and bassoon. The percussion family has a wide range of individual members with unique sounds.

One way we identify an instrument's timbre is by what audio people call the envelope of the sound (how the sound starts, sustains and then ends). Strings, brass, reeds and percussion have characteristic ways of creating their sounds that our brains process quickly and easily.

Another way we identify an instrument's timbre is by the nature of the vibration creating the sound. In this animation I linked down in the post on tone, you can add or subtract individual parts of the vibration and thereby change the overall vibration.

We use this way of changing the components of a vibration to alter its sound all the time when we speak. If you sing a long held note on a particular pitch and go through all the vowel sounds while doing so, it's your making subtle changes to the various components of the overall vibration creating the sound that makes "a's" sound like "a's" and "u's" sound like "u's". 

The specifics of what's going on with the components of the overall vibration are explained by something called the harmonic series, which gets pretty mathematical pretty quickly. At some point in the materials, the harmonic series needs to be explained for those interested. My hope is, though, to help people understand the broad outlines of all this well enough to inform their music making, without inducing math phobia.