When a phrase, clause, or sentence in a line of poetry doesn't finish at the line break but spills over into the next line, that's an Enjambment.
'Endymion' by Keats uses enjambment, as lines 2-4 show:
Its loveliness increases; it will never
Pass into nothingness; but still will keep
A bower quiet for us...
If you try adding enjambment into a poem enter it into one of our Poetry Competitions.