This is a Weltmeister ‘Stella’ accordion spotted in the streets of Barcelona, Spain. Weltmeister used to be the main East German brand (when it was the GDR), made by VEB Klingenthaler Harmonikawerke; nowadays they are made by Harmona.
The accordion is a box-shaped musical instrument of the bellows-driven free-reed aerophone family, sometimes referred to as a squeezebox. A person who plays the accordion is called an accordionist.
It is played by compressing or expanding a bellows whilst pressing buttons or keys, causing valves, called pallets, to open, which allow air to flow across strips of brass or steel, called reeds, that vibrate to produce sound inside the body.
The instrument is sometimes considered a one-man-band as it needs no accompanying instrument. The performer normally plays the melody on buttons or keys on the right-hand manual, and the accompaniment—consisting of bass and pre-set chord buttons—on the left-hand manual.
The accordion is often used in folk music in Europe, North America and South America. It is commonly associated with busking. Some popular music acts also make use of the instrument. Additionally, the accordion is sometimes used in both solo and orchestra performances of classical music.
The oldest name for this group of instruments is actually harmonika, from the Greek harmonikos, meaning harmonic, musical. Today, native versions of the name accordion are more common. These names are a reference to the type of accordion patented by Cyrill Demian, which concerned “automatically coupled chords on the bass side”.