Mester de juglaría ("Ministry of jongleury") is a Spanish literature genre from the 12th and 13th centuries, transmitted orally by "juglares" who made their living by reciting and singing these stories for the recreations of nobles, rulers, and the general public.
These were people of humble origins, traveling comedians who also engaged in circus acts like juggling, tightrope walking, and acrobatics, or acted as clowns who told jokes or played simple instruments, or danced and sang versions of simple mime or puppet pieces, or, importantly, recited verses composed by other authors, called troubadours, either in public places (town squares, above all), or in castles of feudal lords for whom they were housed; much of the time they also supported themselves by the visual arts.
There was the remedador who was dedicated to imitation; the cazurro who practiced the plebeian arts; the juglar de gesta, the goliardo, somewhere between student and vagabond, who understood musical instruments and how to compose for them.
Also included in the word is the concept of a musician, the types of which were quite diverse, from tavern singers and the richly adorned ones who sang in palaces and accompanied nobles on voyages, to those who sang and played dramas in churches with all sorts of musical instruments (the flute, the dulcimer, the drum, and handheld stringed instruments like the vihuela or the rabel).
Compared to the Mester de Clerecía the authors weren't educated, treated popular topics, used simple language and the metrics of the verses is irregular.