What are some characteristics of Imagist poetry? In what way is Williams' "This is just to say" an Imagist poem?

The Imagist poets were a group of early twentieth century writers, primarily from the United States and Britain. A defining publication of the movement was the anthology Des Imagistes, published in 1914 and including the work of William Carlos Williams, Amy Lowell, and Ezra Pound, inter alia. The movement's tenets were that one should treat objects directly, avoid excess verbiage, and follow a musical pattern rather than excessively regular meter.
Williams' poem "This is just to say" is one of the most frequently anthologized and taught Imagist works. It follows the conventions of using extremely simple, conversational language and is written in free verse. The plums of the poem are mentioned directly. Although Williams' act of eating them can evoke elements of human relationships, they are real rather than symbolic plums, presented directly rather than symbolically or allusively.