Iambic pentameter is poetry where the syllables line up in an unstressed/stressed fashion and there are 5 of those unstressed/stressed feet per line.
Shakespeare often used iambic pentameter rhyming couplets in his writing, but he was also fond of using Blank Verse in iambic pentameter.
Blank verse is simply iambic pentameter with the same rhythm but no rhyme scheme.
An example of this is this speech from the prince in Romeo and Juliet:
Rebellious subjects, enemies to peace,
Profaners of this neighbour-stained steel,--
Will they not hear? What, ho! you men, you beasts,
That quench the fire of your pernicious rage
With purple fountains issuing from your veins,
On pain of torture, from those bloody hands
Throw your mistemper'd weapons to the ground,
And hear the sentence of your moved prince.
Three civil brawls, bred of an airy word,
By thee, old Capulet, and Montague,
Have thrice disturb'd the quiet of our streets,
And made Verona's ancient citizens
Cast by their grave beseeming ornaments,
To wield old partisans, in hands as old,
Canker'd with peace, to part your canker'd hate:
If ever you disturb our streets again,
Your lives shall pay the forfeit of the peace.