Final answer:
Tone focus is the primary pitch that is heard when a vibrating system, such as a musical instrument, is played.
Step-by-step explanation:
In physics, tone focus refers to the concept of resonance in a vibrating system, such as a musical instrument.
When a vibrating system, like a string on a guitar, is plucked, it produces a fundamental frequency, which is the lowest natural frequency of vibration.
This fundamental frequency is often referred to as the tone focus because it is the primary pitch that is heard.