A metrical foot that consists of two stressed syllables followed by an unstressed syllable. An example from Phillip Brooks's poem, "Christmas Everywhere", is a good example:
|“|| Everywhere, everywhere, Christmas tonight.
Christmas in the lands of the fir-tree and pines.
1 and a 2 and a 3 and a 4
In a way, it is the reverse of the anapestic (a metrical foot that is two unstressed syllables followed by a stressed.)