Traditional French poetry shares some of the terminology of English poetry, but because of language peculiarities and historical developments, differs from it in many respects. The most obvious difference is that French, not having the tonic accent of the Germanic languages, but a weak final accent, ignores things like iambic pentameter, since there is no alternance of weak and strong to count. This is best illustrated with these examples (accent indicated by italics):
A horse! A horse! My kingdom for a horse! (Shakespeare, Richard III).
La nature est un temple où de vivants piliers (Baudelaire, "Correspondances").
In the English example, the line is in iambic pentameter (a particularly striking example). The French example is an alexandrine, a line of 12 syllables, which is considered the French verse par excellence, just as iambic pentameter is in English (which the French would call a décasyllabe).
This gives a flowing, liquid quality to French poetry (to anglophone ears, anyway). It does not mean there is no rhythm to a French poem, but it is not structured by intrinsic word rhythm. | 
