The term "accordion" covers a wide range of instruments, with varying components. All instruments have reed ranks of some format, apart from reedless digital accordions. Not all have switches to change registers or ranks, as some have only one treble register and one bass register. The most typical accordion is the piano accordion, which is used for many musical genres. Another type of accordion is the button accordion, which is used in musical traditions including Cajun, Conjunto and Tejano music, Swiss and Slovenian-Austro-German Alpine music, and Argentinian tango music. The Helikon-style accordion has multiple flared horns projecting out of the left side to strengthen the bass tone. The word "Helikon" refers to a deep-pitched tuba.