Sipes are the small slits in the tread blocks of a tyre.

Siping is a process of cutting thin slits across a rubber surface to improve traction in wet or icy conditions.

Siping was invented and patented in 1923 by John F. Sipe, The story was told that John Sipe worked in a slaughterhouse and got fed up with slipping on the wet floors, He found that cutting slits in the tread on the bottoms of his shoes provided better traction than the uncut tread.

Two tyre images one is highlighting the sipes

The image above and to the right has some of its sipes highlighted in red