Full-frame and APS-C refer to the size of the camera sensor, with full-frame sensors being equivalent in size to a 35mm film frame, typically measuring around 36mm x 24mm, while APS-C sensors are smaller, usually around 22mm x 15mm. The larger sensor of a full-frame camera generally offers better low-light performance, a wider dynamic range, and a shallower depth of field, which can create more dramatic background blur (bokeh) compared to APS-C sensors.