Final answer:
A line of poetry or prose in unrhymed iambic pentameter is known as blank verse, which has five iambic feet per line, amounting to ten syllables.
Step-by-step explanation:
Unrhymed Iambic Pentameter
A line of poetry or prose in unrhymed iambic pentameter is called blank verse. This form of writing is characterized by having five iambic feet per line, resulting in a total of ten syllables where each iamb consists of an unstressed syllable followed by a stressed one, which can be represented as da-DUM. Blank verse has been widely used by poets and playwrights including William Shakespeare, as seen in his famous work "Hamlet" with the line "To be or not to be: that is the question," even though it includes an extra unstressed eleventh beat. This line structure lends itself particularly well to meditative and dramatic voices, demonstrated in epic poems like John Milton's Paradise Lost. It's important to note, however, that poetic meter in writing sometimes deviates from perfect regularity to avoid monotony and to maintain natural speech patterns.