A concertina is a free-reed musical instrument, like the various accordions and the harmonica. It has a bellows, and buttons typically on both ends of it. When pressed, the buttons travel in the same direction as the bellows, unlike accordion buttons, which travel perpendicularly to the bellows. Also, each button produces one note, while accordions typically produce chords with a single button.
The concertina was developed in England and Germany, most likely independently. The English version was invented in 1829 by Sir Charles Wheatstone, who filed a patent for an improved version in 1844. Carl Friedrich Uhlig announced the German version in 1834.