Catfacing is a term used to describe a specific type of tomato fruit deformity or malformation.
The severity of catfacing can vary, ranging from minor cosmetic blemishes to more significant deformations that affect the overall appearance and quality of the tomato.
Catfacing is typically caused by environmental factors that affect tomato plants during their early development. Some common causes include cold air temperatures, too-cold soil, fluctuating temps, and exposure to certain herbicides or stress during flowering and fruit set.
These conditions can disrupt the normal growth and development of the tomato fruit, resulting in irregularities in shape and appearance.
The best way to prevent catfacing in your tomatoes
Better Homes & Gardens has a great article about how to prevent catfacing here.
Here's another article on more ways to prevent this issue in your tomatoes.
Photo credit: N. Bell, 2004 from the Pacific Northwest Pest Management Handbook
Catfacing doesn't affect the taste or nutritional value of a tomato, but it can make them less visually appealing to use in culinary applications such as slicing or presenting whole. The flavor and texture of the affected tomatoes are usually unaffected, and they can still be used for cooking, sauces, or other processed tomato products.