Final answer:
The phrase in question is a metaphor, equating music to a source of income for an artist. It captures the essence of essential sustenance represented through music, akin to the primary food sustenance, bread and butter.
Step-by-step explanation:
The phrase "Music is the artist's bread and butter" is a metaphor. In this context, it figuratively suggests that music is the primary source of income or livelihood for an artist, just as bread and butter represent basic food sustenance for life. The term does not directly implicate an apostrophe, personification, or synecdoche, as those involve direct address to an absent or non-human entity, giving human characteristics to non-human subjects, and a part representing the whole, respectively.
Understanding figurative language, such as metaphors, is crucial as it enriches the textual expression by adding depth and meaning, similar to the synthesis of music and poetry as observed in the artistry of musicians like Bob Dylan and Leonard Cohen.