In the above picture, do you see the white flowers on the left? These flowers have immature ovaries. The diagram at the left shows what an inferior ovary is. (If you don't understand which parts are which, visit our Standard Blossom Page.) Therefore, the multiple fruit shown above is composed of many inferior ovaries squeezed together. The multiple fruit did not develop from just one blossom the way most fruits do.
Be sure to notice the difference between what's happening with the above multiple fruit and the aggregate fruits described on our Aggregate Fruit Page. Aggregate fruits develop from one flower in which are located several ovaries. Multiple fruits develop when the ovaries of several distinct flowers mature grow packed together.
At the right you see some multiple fruits. They're mulberries from the White Mulberry tree, Morus alba. One neat thing about that picture is that you can see those little black, squiggly things atop 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 ovary 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 point into the cavity and are thus exposed to the cavity's open air. In the picture you can see 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 the hole 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 therefore produce no fertile 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). Both Osage Orange and mulberries are small trees sometimes found in North American towns and both belong to the Fig Family.