What literary term describes a long, narrative poem that usually involves heroic deeds?

The literary term that describes a long, narrative poem involving heroic deeds is "epic." Epic poetry traditionally focuses on grand themes and significant events, often centered around a hero who embodies the values of their culture. These poems typically feature elevated language and formal themes, recounting adventures, battles, and the hero's journey while also reflecting on universal concepts such as honor, courage, and fate.

In contrast, a sonnet is a structured form of poetry consisting of 14 lines with a specific rhyme scheme, primarily focusing on themes like love or nature. An epithet is a descriptive term or phrase used to characterize a person or thing, often appearing in various forms of literature to emphasize particular qualities. Iambic pentameter is a specific metrical pattern consisting of five feet per line, each foot containing an unstressed syllable followed by a stressed syllable, commonly used in sonnets and other forms of poetry, but it does not convey the narrative or thematic depth associated with epics. Thus, epic is the term that best fits the description provided in the question.