https://www.techradar.com/news/best-full-frame-camera

Most entry-level and mid-price DSLR and mirrorless cameras sport an APS-C sized sensor, with the physical dimensions of the chip measuring 23.6 x 15.7mm (22.2 x 14.8mm on Canon cameras). 

A full-frame sensor on the other hand has larger dimensions of 36 x 24mm - the same size as a frame of 35mm film, hence the name 'full-frame', and offering a surface area 2.5x larger than an APS-C sized sensor.