In linguistics, stress or accent is the relative emphasis or prominence given to a certain syllable in a word or to a certain word in a phrase or sentence). Stress is a quality of vowel sounds and has three primary characteristics: length, volume, and pitch. Stressed vowel sounds are longer, louder, and/or higher in pitch than vowel sounds without stress. Every multi-syllable English word contains at least one stressed syllable, and the position of word stress in a word may depend on certain general rules applicable in the language or dialect in question, but in other languages, it must be learned for each word, as it is largely unpredictable).

Listeners rely on stress as a way to identify words, and stress and syllables are closely related. Almost all syllables in English contain a vowel sound; therefore, we usually say that syllables are stressed or unstressed. In spoken language, grammatical words usually do not receive any stress, while lexical words must have at least one stressed syllable. Unlike sentence stress, which frequently changes position according to the speakers intention, word stress tends to be fairly invariable.

Some longer words may have more than one "strong syllable," but one of them tends to stand out more than the other, and they are referred to as primary and secondary stress, respectively. Stress is usually represented in the phonemic chart and transcription by the symbol /ˈ/ placed before the stressed syllable. In words that have secondary stress, the symbol /ˌ/ is included before the appropriate syllable.

In summary, stress in English refers to the emphasis or change in pitch in pronouncing a specific syllable in a word. It is a quality of vowel sounds and is closely related to syllables. Correct placement of stress is important for clear, accurate pronunciation of all English words, and listeners rely on stress as a way to identify words.