Iamb (foot)
An iamb /ˈaɪæm/, or iambus, is a metrical foot used in various types of poetry. Originally the term referred to one of the feet of the quantitative meter of classical Greek prosody: a short syllable followed by a long syllable (as in "delay"). This terminology was adopted in the description of accentual-syllabic verse in English, where it refers to a foot comprising an unstressed syllable followed by a stressed syllable (as in a-bove).
Read more about Iamb (foot): Etymology, Accentual-syllabic Use