The young woman says, "July is over,
but you don't have to go on and
on about it. There's always August."
And with these three lines, I'm prepared to lay out the difference between using an end-stop or enjambment at the ends of your lines. Want to really impress and flatter a fellow poet at the same time? All you need to do is talk up their wonderful use of enjambment.
Lines 1 and 3 in the above example use an end-stop, which just means that your line finishes its thought (often with the use of punctuation) before moving on to the next line.
Line 2 uses enjambment by running over into line 3. That's right, enjambment is when you run your idea from one line into another (or many others).
So, why use one over the other? Well, the way you use end-stops and enjambment can affect the speed readers move through your poem. End-stopping tends to slow down the pace, while enjambing picks it up. Personally, I like to mix it up some to achieve certain effects within my poems, especially if I want to emphasize certain ideas or images.
If you haven't tried using end-stops and enjambment before (or haven't thought about it since "the good old days" of school), then you might want to try playing around with these tools in your poems. If nothing else, you can now start complimenting other poets' end-stops and enjambments--and actually know what you're talking about.