Metre    

The term prosody refers to the study of versification.  Most prosody begins with an analysis of metre. Metre (or meter) is derived from the Greek word for "measure."  The metre is the pattern of stressed and unstressed syllables in  verse.  While there may be some variation or substitution, the number of syllables, and the number of stressed/unstressed syllables remains relatively consistent from line to line. 

The most common metres include:

• anapestic - From the Greek word meaning "beaten back," the anapestic meter consists of two unstressed syllables followed by a stressed syllable.   (The opposite of dactylic)  It is used to create the illusion of running, galloping, swiftness or action.  Take for example, Poe's "Annabel Lee":   "  For the moon |  never beams,| without bring|ing me dreams|\"
• dactylic - From the Greek word for "finger," the dactylic meter consists of an stressed syllable followed by two unstressed syllables.  The dactyl produces a falling rhythm, which is not natural to English.  Therefore, it is relatively rare, used mostly as a counterpoint to another metric form.  This example is from Alfred Lord Tennyson's "The Charge of the Light Brigade":   "Cannon to | right of them,|\Cannon to | left of them,|\ Cannon in | front of them|\..."
• iambic - A two syllable metre, composed of an unstressed syllable followed by a stressed syllable.  The word "defeat" is a prime example of iambic metre.  The iambic metre is thought to be closest to the normal human speech pattern it is also the commonest form of metre because it fits the English language so well.  Thought to have been originated by Archilochus in the 7th century BC.
• paeonic - A metric foot of one stressed and three unstressed syllables.   Common in Classic Greek poetry, it is rare in English.
• spondaic (spondee) - The spondee is a foot composed of two stressed syllables.  Words like daylight and carpool are spondaic.
• trochaic (throchee) -A trochee is a foot composed of one stressed syllable followed by an unstressed syllable.  The words party and bummer are trochees.
• pyrrhic - Another rare foot (some critics even deny this is a foot), the pyrrhic foot is composed of two unstressed syllables

A metrical unit of a line is called a foot.  A foot consists of one stressed syllable and one or more unstressed syllables.  Each type of foot is denoted by a specific term (line breaks are indicated by "/"):

• monometer - indicates one foot per line.  An example can be seen in Robert Herrick's "Upon His Departure Hence":  Thus I / Pass by / and die. / As one / Unknown / And gone; /I'm made / A shade, / And laid / I'th grave, / There have /My cave. / Where tell / I dwell / Farewell.
• dimeter indicates a line that contains two feet.  The third and fourth lines of limericks are dimeter.  For instance:  "Her position to Titian / suggested coition/"
• trimeter - trimetric works have three feet per line.  This example is from Browning's "home Thoughts From Abroad" (feet are separated by | ):   "Oh to | be in | England |/ Now that | April's | there./
• tetrameter - A line with four feet.  Frequently seen in English verse as iambic or trochaic.  This example is from Milton's "L'Allegro":  "Haste | thee nymph, | and bring | with thee\  Jest | and youth|ful Jol|lity."
• pentameter - The five foot line is the basic line in most poetry, especially English verse, blank verse, and the heroic couplet.  It's development is credited to Chaucer.  The following example is from Robert Loews's "Mr. Edwards and the Spider":  "I saw | the spi|ders mar|ching through | the air,/   Swimming | from tree | to tree| that mil|dewed day. . .\"
• hexameter -  the six foot line is very rigidly constructed, being built from four dactyls or spondees followed by a dactyl and then a spondee or a trochee.  This example is from Yeats' "The Lake Isle of of Innisfree":  I will a|rise and | go now, | and go | to Inn|isfree, \  And a small | cabin | build there, | of clay | and wat|tels made ...|\"
• heptameter - the septenarius or seven foot line.  This example is from Kipling's "Tommy":   "I went | into | a pub|lic-'ouse | to get | a pint | o' beer,|\ The publican | 'e up | an' sez, | "We serve | no red|-coats here."|\
• octameter  - A rare eight footed line.  The most common example is Poe's "The Raven."

Meter is usually described as either the dominant foot (which foot is used most often to the strongest effect in a work),  Or the dominant number of feet per line.   Generally, though, critics combine the dominant foot and number of feet to describe meter.  That is were common terms like iambic pentameter and trochaic tetrameter gain their critical meaning.