What is an emjambent in Englishliterature? And the effect of it?

A Poetry line that has no line break but up to the second line break.

Explanation:

It means to step over or putting legs across; coming from the same word in French as in poetry, there are the no terminating punctuation marks lines and these clauses or lines (phrases) it doesn't break at the end of the line as usual therefore it breaks over the next line or couplet.