The term "excellent chemistry" is an idiomatic expression that refers to a strong, positive and harmonious relationship between two or more people. It implies that there is mutual understanding, respect, trust, cooperation and attraction between them. In other words, it means having good rapport with someone else, being able to communicate effectively, share ideas, work towards common goals and enjoy each others company. The phrase can also be used in a broader sense to describe the compatibility or synergy between different elements such as teams, organizations or systems that are working well together.