A tabby is any cat that has a distinctive coat that features stripes, dots, lines or swirling patterns, usually together with a mark resembling an "M" on its forehead. Tabbies are sometimes erroneously assumed to be a cat breed.
In cat genetics, pattern is unrelated to color, and so the tabby coat pattern can show up in combination with a variety of coat colors, including tortoiseshell. Tortoiseshell Tabby cats are often called 'Torbies'). A cat's coat can be described as red tabby or gray tabby.

en.wikipedia.org/wiki/Tabby_cat