What is "th-stopping"

Th-stopping is the realization of the dental fricatives as stops—either dental or alveolar—which occurs in several dialects of English. In some accents, such as some Irish English, Indian English, and much of the working-class English in North America and sometimes southern England, they are realized as the dental stops and as such do not merge with the alveolar stops . Thus pairs like tin/thin and den/then are not homophonous. In other accents, such as Caribbean English, Nigerian English, and Liberian English, such pairs are indeed merged. Th-stopping occurred in all continental Germanic languages, resulting in cognates such as German die, "the", and Bruder, "brother".