Iambic pentameter is a term describing a line of verse with five units (or feet) of iambic meter. This kind of meter contains one unaccented syllable followed by an accented syllable as in the word "award," where the accent is on the second syllable.
Shakespeare's plays are written in unrhymed iambic pentameter, which is called blank verse. In Act 2, here's an example:
Lady Macbeth says to Macbeth after Duncan's murder:
"And wash this filthy witness from your hand."
When we divide the verse into iambic feet, the line looks like this:
And wash | this fil|thy wit|ness from |your hand
You can see five feet of iambic meter; each foot has one unaccented syllable followed by an accented one.
Try this line from Act 3, scene 2 when Macbeth speaks to Lady Macbeth:
Things bad begun make strong themselves by ill