In essense, it is a concertina.

You can summarize as follows:

- If the buttons or keys move in the same direction as the bellows, it is a concertina.

- If the buttons or keys move perpendicular to the bellow, it is an accordion.

-David

It has been my understanding that a concertina does not have chord buttons, that the chords are formed by pressing the individual note. You can see this in one of the videos.

An accordion plays notes on one side and single button notes and cords on the other.

Do they make concertinas that play single button cords?

There are a few concertina looking instruments that have chord buttons. They usually seem to be eight bass, two row diatonic accordians or the Italian one-and-a-half row forced into a 6 sided concerina shape. There is also a version of a Bandoneon called, IIRC, a Bandonika which, again is a diatonic accordian in concertina clothing.

My personal preference (and seems totally logical to me) is that if one button produces a chord it's an accordian, if it doesn't it's a concertina (except that free bass piano accordians would be reclassified as a concertina ).