It is generally agreed that languages can be roughly divided into two categories: stress-timed and syllable-timed. As a definition of each, we can say that in syllable-timed languages, syllables tend to follow each other at regular intervals, with an equal amount of time being allocated for each syllable. In stress-timed languages, on the other hand, stresses tend to occur at regular intervals, with the result that the remaining unstressed syllables, no matter how many in number, have to be squeezed in between the stresses to accommodate the regular beat of the stress.
Some stress-timed languages: English, Swedish, Russian, Arabic, European Portuguese.
Some syllable-timed languages: Spanish, French, Italian, Japanese, Finnish, Brazilian Portuguese.