The word stupa can be translated in quite a few ways. In Hinduism it means to raise or a 'pile of clay', in Greek a stump or block and in sanskrit a 'tuft of hair'. Eventually, to Buddhists, stupa became the name of the cone shaped religious monument that was used to store sacred relics of the Buddha or saints.
Buddhism in Cambodia intermingles with pre-Buddhist animist and Brahman beliefs so much so that it sometimes barely resembles the Buddhism of the rest of the region. Cambodians, for example will eat everything and Cambodian monks usually collect money on their morning rounds rather than food.
Stupas to Cambodians are gravestones for anyone who can afford one. Bigger and more fancy stupas belong to wealthier families. They are often family memorials rather than for an individual and usually have the ashes of the deceased in a small door near the base of the stupa which is opened periodically by the family so they can place offerings inside to placate their ancestors.
Karen asked yesterday where I get my information from and the answer is really everywhere. I have an academic background in Anthropology and World Religion so some (like the general bits of this blurb) come from a lifetime of reading and talking to anyone I can engage. When we first arrived in Cambodia it dawned on me that Buddhism here was unique and specific information is not easy to come by since so much of the written and human knowledge was destroyed by the Khmer Rouge. Many Cambodians don't know that their beliefs are so different from their neighbours (and would never consider giving up eating meat for example) and they don't know why or where their beliefs come from. Our driver faithfully observes religious days by taking food to the 'pagoda' but doesnt know exactly why or how one festival differs from another. He does it because his ancestors ghosts will be angry if he doesnt.