The phrase "What is" is commonly used in English to ask for definitions, explanations, or descriptions of something. It is a basic interrogative phrase that initiates a question about the nature, identity, or meaning of a subject

. Additionally, "What is love?" is a famous phrase popularized by the 1993 dance hit by Haddaway, which explores the emotional and relational aspects of love in a catchy, memorable way

. This phrase has also been used in various music and cultural contexts, reflecting on the concept of love. If you meant something more specific by "What is," please clarify so I can provide a more detailed answer.