Theories that analyze a given item as a mere bundle of items of some other kind; where the first item would normally be thought of as something substantive and independent, the other items being somehow related to it, or dependent on it and owing their existence to it.
There are two main examples.
The first treats ordinary objects as mere bundles of properties, so that my chair is simply a set of properties (blackness, four-leggedness, and so on) somehow put together, there being no independent chair that has these properties.
The second example treats the mind or self as simply a set of experiences and not as something which has these experiences.
David Hume, A Treatise of Human Nature (1739-40); see book 1, part 1, §6 for bundle theory of the self (which, however, Hume withdraws in the Appendix)