Merriam-Webster defines "well-being" as "the state of being happy, healthy, or prosperous."
Unlike wellness, which mainly focuses on physical health, well-being takes into account how satisfied a person is as a whole, both body and mind. It's centered around the belief that physical, emotional, and spiritual health all play important roles in your overall health, happiness, and satisfaction.
For this reason, well-being may look different for everyone. What makes one person happy and fulfilled in life isn't necessarily what makes another person feel happy and fulfilled. For one person, healthy personal relationships may have a larger impact on their well-being, whereas a thriving career may be more important to the well-being of another person.