Your pharynx is the part of your throat that lies right behind and below your tongue, but above your larynx (or voice box or Adam’s Apple). Your pharynx stretches sideways when you are in the middle of a big yawn.
The pharynx is a great shaper of tone, When you widen it, for example, while you sing, you get a richer, thicker, more R&B sound. If you carefully constrain it, you get more of a thin folk or country sound.
Getting control of the pharynx is tricky, and it is kinda lazy and not used to working except when yawning. If you imagine laughing silently (like you are at a funeral), you’ll feel it widen. Just practice gaining more control over it and keeping it wide for longer periods.