I have a wonderful book called, "Come let us drink, Catches, Compleat, pleasant and Divertive, contriv'd by the late famous Mr. Henry Purcell." c 1972 Galliard Ltd. The editor, Michael Nyman states in his intro: " . . .From the 1630s on, the round, or catch as it had exclusively become, was taken up by the established composers of the time.   . . .Many of these catches are harmonically insecure, rambling & of a distinctive tunelessness. Purcell's, despite the obvious limitations of the form, are extremely attractive melodically, complex in texture, and marvellously characterised dramatically.
   Attempts to distinguish the round from the catch usually hinge on some minor musical or verbal technicalities. A round is continuous, the second voice follows on from the first without a cadential break; the catch on the other hand is sectional. . . .The catch, with its 8, 12 or 16 bars units (as against the round's 1. 2 or 4) was of necessity more poised and cadential.
   The distinction made between rounds and catches on purely verbal grounds is shaky. A catch is said to be a round which, by careful arrangement of the voices, produces hidden meanings (double entendres) when the voices are heard in combination which are not apparent when the text is read in linear sequence. . . .
The catch was a means of self-expression for the liberated middle class drinking man--it revolved around three subjects: sex, drink and politics. "
   
    These Catches by Henry Purcell are quite bawdy. [Purcell, born in 1659, & died when Bach was 10, but both are considered to have lived during the Baroque period] They were written around 1680. A couple were based on poems by a known poet of the time. They were not for the voice only, as the rounds usually were. They were often written with basso continuo accompaniment, sometimes with flute, guitar, or whatever.
   So, Catches were PUB/BAR SONGS that men in pubs sang, in 3 or 4 part harmony. The book was given to me when I was in college, & I have no idea if it is still in print. The fellers in the Symphonia frat had a great time singing them when I let them borrow the book.