Short answers, pulled from the story.
A guild is a professional association of artisans and merchants who oversee the practice of their craft or trade in a particular territory. Its key privilege was that only guild members were allowed to sell their goods or practice their skill within a city, often alongside controls on prices, trading hours, and the number of apprentices.
Guild-like organizations reach back to the ancient world. Around 2254 to 2218 BC, Naram-Sin of Akkad set common Mesopotamian standards used by artisan guilds in each city, and Ancient Rome had associations called collegium or corpus, including the corpus naviculariorum of merchant mariners at Ostia.
Women did participate in medieval guilds, though most craft and trade guilds were male-dominated and usually admitted women only through marriage or as widows or daughters of masters. In Rouen, women had worked as full-fledged masters in 7 of the city's 112 guilds since the 13th century, and Etienne Boileau's Livre des metiers records several Parisian guilds as female monopolies.
Enlightenment thinkers such as Adam Smith argued that guild monopolies inhibited free trade and innovation, and centralized nation-states weakened guild control through new patent and regulatory systems. The French Revolution abolished guilds in 1791, and most European countries followed during the 18th and 19th centuries as industrialization made guild-based production less viable.
Modern American guilds include film and television bodies like the Screen Actors Guild, the Directors Guild of America, and the Writers Guild of America, plus state bar associations for lawyers and state Medical Boards for doctors. The Newspaper Guild is a labor union for journalists with over 30,000 members in North America.
Guild-like organizations developed across the world in many forms. India had corporate bodies of craftsmen and traders called sreni, the Ottoman Empire had the Akhiya fraternities, late-imperial China had the gongsuo, Japan had the za and later kabunakama, and the Aztec Empire had merchant guilds known as the pochteca.
In the City of London, medieval guilds survive as livery companies, whose senior members elect the sheriffs and approve candidates for Lord Mayor of London. With the livery companies, the UK has over 300 extant guilds and growing, and the Preston Guild Merchant still admits descendants of burgesses into membership.