The melodica is a free-reed instrument similar to the accordion and harmonica. It has a musical keyboard on top, and is played by blowing air through a mouthpiece that fits into a hole in the side of the instrument. Pressing a key opens a hole, allowing air to flow through a reed. The keyboard is usually two or three octaves long.
The instrument was invented by Hohner in the 1950s or 1960s,  although it is also claimed that it was invented by the Brooklyn musician Joseph Lederfine in order to teach music fundamentals to children. The melodica was probably first used as a serious musical instrument by jazz musician Phil Moore Jr. on his 1969 Atlantic Records album Right On. . It is most often associated with Jamaican dub and reggae musicians in the 1970s, most notably Augustus Pablo.  Henry Slaughter (of The Imperials) played a melodica solo on "I'll Remember You," which was recorded by Elvis Presley on June 10, 1966 and appeared on the album "Spinout."
...Popular melodica manufacturers include Sound Electra, Angel, Hohner, Suzuki, Yamaha and Samick. It is also known by various names such as melodion (Suzuki), melodia (Diana), pianica (Yamaha), mylodica (Sound Electra), "melodihorn", or clavietta.
Melodicas are portable enough to be carried around. They have been very popular in music education, especially in Asia.