What is the origin of the idiom "last word" and when to use it?

The idiom "last word" originated in the early 19th century and is used to describe something that is considered the most fashionable or advanced in comparison with others of the same type. The phrase implies that the particular item, idea, or concept represents the ultimate or definitive expression within its category. It is used to suggest being at the cutting edge, the most recent development, or the pinnacle of excellence, often in terms of style, technology, or innovation.