What the difference between these 2?
Matched-pairs design is a special case of randomized block design. If the “blocks” we make contain only 2 individuals paired up, it’s matched-pairs. Similarly, if EVERY individual gets BOTH treatments (for example, apply lotion A to your left arm and lotion B to your right arm; compare the results), then it’s matched pairs as well.
But if the blocks contain lots of individuals, this is not matched pairs.