An iamb is a metrical foot that consists of one unstressed syllable followed by one stressed syllable. Lines composed of five iambic feet are called iambic pentameter. Examples of iambic pentamer include the plays of Christoper Marlowe and William Shakespeare, John Milton's epic "Paradise Lost" and various poems as disparate in outlook and technique as William Wordsworth's "Tintern Abbey," Alfred, Lord Tennyson's "Ulysses" and Wallace Stevenson's "Tea at the Palaz of Hoon." Many English words themselves are natural iambs: for instance, you pronounce "content" (in its adjectival sense) as "con-TENT." You can represent an iamb using an "x" and a "/", as in the following line from Alexander Pope's "Eloisa to Abelard":
x / x / x / x / x /
How ha - ppy is the blame - less vest - al's lot
Here the "x"s indicate unstressed syllables, and the slashes indicate stressed syllables.
A trochee is a metrical foot consisting of the a stressed followed by an unstressed syllable. This means it is the opposite of an iamb. Scholars generally consider trochees blither and gentler than iambs, and poets often employ trochaic meters in light verse. One famous example of trochaic pentameter used for a very different effect, however, is the following line from Act III of Shakespeare's "King Lear":
/ x / x / x / x / x
Ne - ver, ne - ver, ne - ver, ne - ver, ne - ver.
A dactyl is a metrical foot composed of three syllables: one stressed syllable followed by two unstressed syllables. English poets nearly always use the dactyl in conjunction with other metrical feet, as in the first line of Walt Whitman's "Out of the Cradle Endlessly Rocking":
/ x x / x / x x / x
Out of the cra - dle, end - less - ly rock - ing
First a trochee follows an initial dactyl, and Whitman repeats the pattern.
In Episode I of "Ulysses" Stephen Dedalus's roommate Malachi "Buck" Mulligan proudly announces that his name is comprised of "two dactyls." A natural dactyl in English is the word poetry, which we pronounce "PO-etry."
An anapest is a three-syllable foot comprised of two unstressed syllables followed by a stressed syllable. A very famous example the use of anapests in English poetry is William Cowper's "The Solitude of Alexander Selkirk," in which Cowper employs anapestic trimeter, lines of three anapests:
x x / x x / x x /
I am mon - arch of all I sur - vey
Poets often use anapests, like trochees, in light or comic verse. T.S. Eliot wrote much "Old Possum's Book of Practical Cats" in variety of anapestic meters, and Dr. Seuss employed it in most of his children's books.