Well there's divided view about this. some people think that particles and waves are both two facets of a larger more sort of 'androginous' form of stuff and we see different sides depending on the circumstances. others say everything is particles but sometimes exibit properties that we think of as wavelike. So you could think of a particle as a highly condensed wave of energy, if you wish. i like that idea, wether it has any scientific merit i don't know. otherwise there's the shrodinger equation that defines the probability for the location of a particle. this assumes that a particles mass and momentum are not spread out like a waves but is infact in one spot that can be measured, its just until you measure it the probability of finding it in a space is spread out over that space, which is more or less the basis for many quantum things
hope this helps
-G