When someone says something "is a mood," they are using a colloquial and informal expression to convey that a particular thing or situation resonates with their current emotional state or reflects a specific vibe or feeling they have at that moment. It suggests that the thing being referred to captures the essence of their mood or represents how they feel in a particular situation.
For example, if someone posts a picture of themselves relaxing on a beautiful beach with a carefree expression, and they caption it "this view is a mood," they are saying that the scene captures the laid-back and happy feeling they have in that moment.
In essence, saying something "is a mood" is a way to express a strong emotional connection or similarity between oneself and what is being observed or experienced. It has become a popular phrase in internet and social media culture, often used to relate to others or express oneself humorously.