There is no single definition for what a chest voice is but the most common use of the term refers to the natural singing or speaking voice that you use. Bust out the loudest note that you can right now and that would be singing with your chest voice.
The head voice is one step above the chest voice and is slightly higher. The name originated because it feels to a singer as if the notes they are singing are resonating in their head.
Everybody has both of these voices as well as a falsetto. While the chest voice is, in fact, your natural voice that doesn’t mean that you don’t need to work on improving this vocal range.
How to Work on Your Chest Voice
The chest voice, just like the other voices, can be improved by practicing vocal sounds in that range. If you stronger arms you work out your arms. The same applies for your voice. With that being said, here are some vocal exercises that can help you achieve a stronger chest voice. One great exercise is saying “mum mum mum mum mummmm” with the last “mum” being held out for a few seconds. Each mum should be one note lower than the previous. Progressively lower the scales until you cannot get any lower. Be sure to quit if you start to feel too much of a strain as this is a sign that you have gone too far below your range. You want to get as low as possible without damaging your voice. There is a fine line between your lowest note and the note too low for you but it does exist and you will be able to tell when you have hit that limit.
A second exercise to perform is simply scales using Do Ti La So Fa Me Re Do. Repeat and get progressively lower each set.
Practice other singing exercises that you know while singing with your chest voice. If you progress upward into higher notes you will reach your head voice and finally your falsetto. It is important as a singer to be able to transition from one voice to another smoothly. Not every song has notes that are only in your chest voice range. In fact, most songs you sing are going to require you to sing in multiple vocal ranges. Not being able to transition from one voice to another is an extreme disadvantage and will prevent you from reaching your maximum singing potential.
The switches between your three different “voices” will probably not be smooth when you first start out. This is fine and completely normal. This is why you must practice often and correctly. Only then will you be able to effortlessly transition from one voice to another.