A pause within a line of a poem is called a "caesura." It is a literary device used in poetry to create a break or pause in a line of verse, often marked by punctuation like a comma, semicolon, or dash. The caesura is used to add emphasis or create a particular rhythm in the poem. It is also used to add variety to the poem's structure, as it allows the poet to break up long lines and add more nuance to the poem's meaning.