A recorder is a musical instrument about a foot long played by blowing through a whistle-like mouthpiece known as a fipple, and placing fingers on holes to stop air from coming out.
Baroque and Renaissance music written "for flute" would have been played on a recorder. The modern "flute" (transverse flute)— these days made of silver, held sideways, and played by blowing across it— was not developed until the late 17th, early 18th centuries.
The recorder and the modern flute are members of the woodwind family. Other woodwinds, like the clarinet, saxophone, and oboe, have reeds, which gives them a kind of sharp and buzzy sound. The recorder and flute are reedless, and have a very sweet, pure sound.
Recorders are used in music education, because it is easy for beginners to play recognizable tunes on them. The use of recorders in education was popularized in the United States in the 1950s by the Trapp Family Singers, the family depicted in The Sound of Music. "Song flutes," "flutophones," and "tonettes" are really just slightly modified recorders.
The familiar small recorder is actually only one member of the recorder family: the soprano recorder. Increasingly larger and lower-pitched members of the family include the alto, tenor, and bass recorders.