"Lovers' Infiniteness" by John Donne has two different meters contained within the poem.
The poem itself is made of three stanzas. Each stanza is 11 lines long. The rhythm of the poem is iambic. That means that an unstressed syllable is followed by a stressed syllable. Iambic rhythms are an easy rhythm for a reader to follow and can give many poems a "sing-song" quality.
Donne utilizes a combination of eight-syllable lines and ten-syllable lines. With the iambic rhythm, that makes the poem's meter iambic pentameter and iambic tetrameter. A single unstressed syllable with its stressed partner makes a single "foot" of poetry. So a line with 8 syllables in the iambic foot totals 4 feet in a single line. Hence the iambic tetrameter. 10 syllables is 5 feet, or pentameter.