The simplest explanation for tire tread will be that they’re the ‘grooves’ in the tire that not just make it look good bit also perform the vital function of draining away water from under the contact patch. The larger tread of ‘knobby’ tires allows the knobs to dig into the soft ground and provide grip where the smoother tread pattern would not grip.
Talking of tread patterns, few know that tires have sea and land within. These are the technical names of tread features. The grooves are the ‘sea’ while the raised rubber surrounding them is the ‘land’. These land and sea patterns are usually unique to each tire model and most tire manufacturers favor a certain family of patterns compared to others.