Iambic pentameter means literally the iambic '2 beat' multiplied by 5 (penta) usages of the iambs. This gives a standard 10 syllable line. (2x5=10) Shakespeare was the user par excellence of iambic pentameter. However, Shakespeare's usage was closer to musical note/beat measurements. Shakespeare used a variation of iambic pentameter which allowed for equal measures, but also allowed for expression, like the different note values adding up to the value of bar in music. This usage effectively reorganizes the iambic usage into the right emphases, but retains the scansion of the pentameter's 10 beats.
Examples of Iambic Pentameter:
To be, or not to be, that is the question|
You'll notice that the 7th iamb, not the 8th, is the variant. That's because both the expression of the words require it and the last syllable would be overstressed and meaningless. 'Question', if pronounced Question, is simply bad pronunciation, and ineffectual as emphasis. 'Question', however, is normal, and identifies the subject with emphasis.