Quartz is a combination of a man-made and natural product. In the manufacturing process, small- and medium-sized quartz crystals are combined with a resin and any necessary coloring. The mix is then put into a mold, and air is removed as heat and pressure are applied. The resulting product is smooth and extremely durable, but as there is more labor required to create a finished product, it can be more expensive than granite. Quartz countertops are manufactured by a variety of companies such as Caesarstone, Silestone, Zodiac (Dupont), etc.
Some of the pros of quartz countertops are that they are generally more uniform than natural stones (which can also be considered a drawback if you like color variation and veining), quartz is very hard and non-porous, and it is aesthetically less “busy” than granite, which can lend itself to a more contemporary design scheme.
Cons of quartz are that it is equally or more expensive than many types of granite, color options are limited to the manufacturer’s color palette (although these have improved in recent years), seams can be more visible due to less camouflaging variation in the product and installation cost may be slightly more than granite.
Quartz can be a great material for many kitchen remodels, so I encourage you to ask your designer or installer if it might be the right product for you.