Quickfit is a system (and manufacturer) of laboratory equipment, which as its name suggests fits together quickly (and easily).
Objects such as flasks, tubes, bungs and so on are all made of glass. Joints are made from tight fitting etched/sanded glass surfaces, which fit and lock together easily. They form a strong, airtight seal especially when subjected to liquids which can flow into the joints (but not out of them) through capillary-like action.
Quickfit sets of equipment are generally designed for a specific purpose - EG an "organic chemistry" set which contains equipment that can be used for distillation and similar experiments.