"Blank verse" is a term that throws even some students of literature for a loop, at least early in their studies. Basically, it's just iambic pentameter. Of course, if you don't study poetry much or had a bad experience with English in high school, you hear or read "iambic pentameter" and probably want to run away, or at least cover your ears. It sounds so technical and weird, that term.
To review, as much for myself as anyone else: verse in English works by combining syllables and stresses--a "stress" referring to a syllable that's pronounced with greater force than is the syllable before or after it (for example). When most people say "banana," they stress the first "na" more than the "ba" and the second "na." So the first "na" is the stressed syllable of the three.
One iamb (what a weird word) is made of two syllables, and the second of these syllables is stressed. "Alone" is a good example. Almost no one pronounces that word A-lone. Instead they put the stress on "lone."
String five such two-syllable units (iambs) together, and you have yourself blank verse. Easy! What's "blank" about it, aside from the fact that your mind may go blank with all this talk of iambic pentameter? It doesn't rhyme. That's all. So you could write a hundred lines of blank verse and not have to rhyme, although you probably would rhyme by accident at some point.
Iambic pentameter is in some ways the spine of Anglo-North American poetry. You find it in such forms as sonnets, villanelles, and sestinas, for example (the first two forms rhyme, of course, and the third form repeats six end words in a different pattern).
Unrhymed iambic pentameter (blank verse) has its own noble heritage. Shakespeare composed his plays--for the most part--in this verse. Milton used it in Paradise Lost. Wordsworth used it. So did any number of other well known poets. Free verse, which may pay attention to rhythm and sound, certainly, but which doesn't use a regular meter (or pattern), is now the fall-back form of poetry. Open up any literary magazine, and you expect to find free verse. In second position, I think, is blank verse, still.
Blank verse is kind of fun to write (unless you have a life). For poets, it can be like working out is for athletes. Also, the regular old English we speak every day almost "wants" to be iambic pentameter, so you don't have to work that hard to get those alternating syllables going--unstressed/stressed. And there's something conversational about blank verse--one of many reasons, probably, that Shakespeare used it in plays.
Here's a small bit of blank verse on the topic of mistakes:
If each mistake I’ve ever made in this,
My life, were to become a snowflake, drifts
Would rise above the eaves. I’d open wide
The door and look into a blue-tinged bank
Of snow. I’d close the door and say, “I should
Have left last week when I first heard the news
A storm was coming in." I’d light a fire.
The room would fill with smoke, however, for
I’m sure I would have left the damper closed.
One convention of blank verse is to capitalize the first word of every line, even though it may not start a sentence, so that takes some getting used to. Another convention is to pad a line with extra words from time to time to get the quota of five iambs. In this little exercise-poem, I didn't really need to write "wide," but I did because I needed a stress there, and at least "wide" is plausible. Also, I probably could have written simply "in life" instead of "in this/My life," but I padded a bit to keep the meter going.
Note, too, that "My" and "life" receive almost the same stress. All iambs are not created equally. In every line of blank verse there's also a pause that seems to occur "naturally"; the official name for it is a "caesura." Sometimes punctuation causes it; sometimes it doesn't. Milton was great at deliberately moving the caesura into different places in different lines, partly to avoid monotony.
And so I've made more mistakes to add to the pile of . . . snow: discussing "iambic pentameter" and "blank verse," calling up bad memories of high school English for some people, and writing some blank verse for God and Milton and everyone else to see should they stumble down this blind alley (see previous post) of the internet.
Try writing some blank verse, maybe while you're watching TV. When you're done, you will have joined a long line of scribblers stretching back to Shakespeare (and even further). It's a big club. Everybody's welcome.