"Barrel distortion" refers to a type of optical distortion that makes straight lines appear curved or bent towards the center of an image. It creates a bulging effect similar to the shape of a barrel, hence the name. Full definition
There's some mild barrel distortion around the edges of wide shots, but it's a small price to pay for being able to get everyone in. (pcmag.com)
Images look a bit soft overall, especially in low light and there's some noticeable barrel distortion when shooting wide. (techradar.com)
It's a wide angle lens which makes it easy to fit more into the frame but it does suffer from some slight barrel distortion towards the edges. (androidauthority.com)