Here's what that means:
* Iamb: An iamb is a metrical foot consisting of an unstressed syllable followed by a stressed syllable. For example, "again," "be-low," "the-sun."
* Pentameter: Pentameter means "five measures." So, iambic pentameter has five iambs per line, totaling 10 syllables.
Here's an example from Shakespeare's Sonnet 18:
"Shall I compare thee to a summer's day?"
* "Shall I" - unstressed, stressed
* "com-pare" - unstressed, stressed
* "thee to" - unstressed, stressed
* "a sum-mer's" - unstressed, stressed
* "day?" - unstressed, stressed
This pattern of unstressed and stressed syllables creates a natural, flowing rhythm in the poem.
Keep in mind that while the ideal is strict iambic pentameter, there are occasional variations for emphasis or artistic effect.