John C. Wells in the context of "X-SAMPA"

General American English, known in linguistics simply as General American (abbreviated GA or GenAm), is the umbrella accent of American English used by a majority of Americans, encompassing a continuum rather than a single unified accent. It is often perceived by Americans themselves as lacking any distinctly regional, ethnic, or socioeconomic characteristics, though Americans with high education, or from the (North) Midland, Western New England, and Western regions of the country are the most likely to be perceived as using General American speech. The precise definition and usefulness of the term continue to be debated, and the scholars who use it today admittedly do so as a convenient basis for comparison rather than for exactness. Some scholars prefer other names, such as Standard American English, though this can be a wider term encompassing more than just accent.

Standard Canadian English accents may be considered to fall under General American, especially in opposition to the United Kingdom's Received Pronunciation. Noted phonetician John C. Wells, for instance, claimed in 1982 that typical Canadian English accents align with General American in nearly every situation where British and American accents differ.

Estuary English is an English accent, continuum of accents, or continuum of accent features associated with the area along the River Thames and its estuary, including parts of London, since the late 20th century. In 2000, the phonetician John C. Wells proposed a definition of Estuary English as "Standard English spoken with the accent of the southeast of England". He views Estuary English as an emerging standard accent of England, while also acknowledging that it is a social construct rather than a technically well-defined linguistic phenomenon. He describes it as "intermediate" between the 20th-century higher-class non-regional standard accent, Received Pronunciation (RP), and the 20th-century lower-class local London accent, Cockney. There is much debate among linguists as to where Cockney and RP end and where Estuary English begins, or whether Estuary English is even a single cohesive accent.

A lexical set is a group of words that share a particular vowel or consonant sound.

A phoneme is a basic unit of sound in a language that can distinguish one word from another. Most commonly, following the work of phonetician John C. Wells, a lexical set is a class of words in a language that share a certain vowel phoneme. As Wells himself says, lexical sets "enable one to refer concisely to large groups of words which tend to share the same vowel, and to the vowel which they share". For instance, the pronunciation of the vowel in cup, luck, sun, blood, glove, and tough may vary in different English dialects but is usually consistent within each dialect and so the category of words forms a lexical set, which Wells, for ease, calls the STRUT set. Meanwhile, words like bid, cliff, limb, miss, etc. form a separate lexical set: Wells's KIT set. Originally, Wells developed 24 such labels—keywords—for the vowel lexical sets of English, which have been sometimes modified and expanded by himself or other scholars for various reasons. Lexical sets have also been used to describe the vowels of other languages, such as French, Irish and Scots.