It has five metrical feet that each contain an unstressed syllable immediately followed by a stressed one.
Iambic pentameter is a meter that follows a specific structure of 5 iambs. Pent = Five. An iamb is an unstressed syllable then a stressed syllable. These two syllables make up a foot. This set of five feet equals 10 syllables all together. This line from Shakespeare's sonnet has 10 syllables in a pattern of unstressed then stressed syllables.
