In poetry, an end-stopped line concludes with a logical break in grammar and includes some form of punctuation to break the reader to a momentary stop. It contains a thought and brings the reader to a slight pause, at least momentarily. In the example below from Walt Whitman’s “Song of Myself,” note that each line is end-stopped, either with a comma or a period (to end the stanza).
I celebrate myself, and sing myself, And what I assume you shall assume, For every atom belonging to me as good belongs to you.
In poetry, enjambment describes a line that runs over from one into the next. The words that continue on the subsequent line complete the thought that was begun on the previous line. In the example below from William Wordsworth’s “Lines Composed a Few Miles Above Tintern Abbey,” note how the first four lines have enjambment. There is a little tension here because the reader must go forward to the next line in order to complete the meaning of the previous: …with the length (of what? the length of five long winters); …again I hear (hear what? hear these waters); …and connect (connect what? connect the landscape with the quiet of the sky).
Five years have passed; five summers, with the length
Of five long winters! and again I hear
These waters, rolling from their mountain-springs
With a soft inland murmur.—Once again
Do I behold these steep and lofty cliffs,
Which on a wild secluded scene impress
The landscape with the quiet of the sky.
A NOTE ON END-STOPPED LINES AND ENJAMBMENT
Whether you use end-stopped lines or enjambment requires conscious thought. Wordsworth, in the example above, uses both, and his choices have purpose. Not only does he build tension and suspense in the lines, but the lines perform the image he is describing: the image of water flowing down is described in lines that “flow down.” If Wordsworth had adhered strictly to end-stopped lines, it would make the poem feel much more rigid and inflexible; the mixture of enjambment and end-stopped lines brings a “natural” feel to the poem and makes it come alive. (Despite the fact that Whitman uses end-stopped lines, this poem feels “alive” too, largely because his lines do not feel forced into being a consistent length.)
Your choice depends a lot on how you want the reader to experience your poem, but it needs to be a choice. A lack of punctuation in a poem can be profoundly confusing for a reader if the lines do not work together to create and complete ideas. If you are writing lines of poem that contain complete thoughts and complete syntax, then most of the time you should use some punctuation to create an end-stopped line and facilitate the reader’s ability to understand your work.