Period piece

I often hear the phrase "period piece" on home designing shows. When we hear it, we assume fancy-looking 19th century furniture, but really, what does it mean? I looked it up, and it's described as "A piece of furniture, etc dating from, and in the distinctive style of, a certain historical period."

Isn't *every* part of history a "certain" historical period? Right now we're in the 21st century, so couldn't a 20th century piece be considered "period"? Or even a piece of furniture created yesterday?

I'm may be persnickety about it, but if you really think about it, it's an undefined phrase that has emerged with certain assumptions.