Final answer:
Regional differences in language, including pronunciation and grammar, are understood as dialects, accents, or varieties. These distinctions are deeply tied to factors such as geography and ethnicity, reflecting the rich diversity within a language like American English.
Step-by-step explanation:
Regional differences in the phonological system of a language may be referred to as dialects, accents, varieties, or all of the above. These terms encompass variations in pronunciation, grammar, vocabulary, and syntax that are influenced by elements such as geographical location, culture, ethnicity, and socio-economic status. American English, for instance, is rich with regional dialects that might even be as specific as a single city. Examples of this include the pronunciation of "water" as "woohder" in the Philadelphia metropolitan area or the use of the term "yooz" as a second-person plural form. A dialect may carry such strong identity markers for a group that it can be considered a signifier of ethnicity, often blending elements from various languages and evolving over time.