Multlple fruits are actually bunches of fruits growing together, and each fruit has developed from its own flower. An aggregate fruit derives from one flower with several pistils, but a multiple fruit develops when the pistils of several distinct flowers mature and grow packed together.

At the right you see some multiple fruits, some mulberries, of the White Mulberry tree, Morus alba. One neat thing about that picture is that you can see those little black, squiggly things on the bumps of which each mulberry "fruit" is composed. Those squiggly things are the former flowers' stigmas. That make sense because each "bump" was a former pistil in a flower. If you eat a single mulberry you can be grammatically and botanically correct if you say "Those fruits sure tasted good!"

Multiple fruits can be plan weird. For example, at the left you see a fig I just plucked from a tree and cut down the middle. You are seeing a cross section. The fig was attached to its twig by the projection at the far left. In this picture the actual fig flowers are inside the thing you are expecting to be a fruit. The flowers are so immature and enmeshed in the pink, pulpy growth of the receptacle surrounding it that it's very had to see them. Notice that in the center of the multiple fruit there is a cavity. The actual flowers grow so that their tops are exposed to the cavity's open air. You can see some flower stems radiating away from the flowers and the cavity, attaching to the surrounding yellow receptacle. Note that at the fig's far right there appears to be an opening in the receptacle. Among wild figs (this is a domesticated one) the cavities do indeed extend to a hole formed in this area. Wild wasps enter through this hole, go inside the fig and walk around atop the actual fig flowers gathering nectar, and in the process pollinate the flowers. Domesticated figs such as the one illustrated have lost the ability to produce fertile flowers and consequently seeds. Domesticated fig trees are reproduced by making rooted woody cuttings from larger trees. The technical name for the precise kind of multiple fruit the fig is, is syconium.

Though pineapples and figs are the best-known examples of multiple fruits, if you look long enough in your neighborhood you might also see the multiple fruits of  Osage orange, shown at the right (it's about the size of a softball), and mulberries, which are both small trees sometimes found in North American towns. Both mulberries and Osage orange belong to the fig family.