Faience is the French name for the same tin-glazed earthenware tradition known as majolica in Italy: an opaque, usually white, tin- or other-opacified glaze painted with colored decoration on top before a single firing fuses both together.
Faience shares majolica's basic method exactly: an opaque white glaze base is applied unfired, painted directly with metal-oxide pigments while still dry and powdery, then fired once to mature the glaze and fuse the decoration into it at the same time. The name itself is not a different technique, only a different regional name for the tradition as it developed in France and other parts of continental Europe, tracing back to the same Islamic tin-glaze innovation and its spread through Hispano-Moresque ware (see glaze's history).
Faience takes its name from Faenza, an Italian city known for maiolica production, adopted into French to describe the tin-glazed earthenware that French workshops began producing as the tradition spread across Europe, arriving in France during the 16th century and reaching its widest use among elite patrons through the 17th and early 18th centuries, before the later spread of French soft-paste porcelain factories. Rouen has produced faience since at least the 1540s; Nevers, known especially for a distinctive dark cobalt-blue ground called "Nevers blue," produced it from around 1580 into the early 19th century; and Moustiers faience, produced from about 1679, is traditionally said to trace back to a monk from Faenza who shared the tin-glaze technique with a local potter, Antoine Clérissy, whose workshop became the town's most important. Closely related traditions developed in parallel elsewhere in Europe, most notably Delftware in the Netherlands.
Faience is sometimes used as a broader umbrella term in English for tin-glazed earthenware generally, beyond specifically French production, which can cause confusion with majolica and Delftware; all three describe essentially the same underlying tin-glaze technique, distinguished mainly by region and decorative style rather than by any real difference in materials or process.
Dutch Delftware workshops developed a genuine technical refinement on the basic method, known as petit feu ("small fire"): rather than confining decoration to the pigments able to survive the main glaze firing, gold and certain delicate enamel colors, reds especially, that would burn out at that temperature were painted on afterward and fixed with a third, much cooler firing (around 600°C) in a small dedicated muffle kiln. This let a piece carry colors the single-firing method could never have reached, at the cost of an entire extra firing cycle just for those additional colors.