The concept of realization is central to the physicalism program for both Poland and Melnyk. As it is more clearly laid out and (I think) more useful, I will follow Melnyk's version.
For Melnyk (p.26)
Every object is either an object of some physical kind or a physically realized object of some functional object kind.The same goes for properties and events: they are either physical or physically realized. The physical, as we have seen, is for Melnyk simply that which is describable in the proprietary language of fundamental physics. But what does it mean for something to be physically realized?
For Melnyk, higher-order types are functional types that are defined via an associated condition. A lower-order object (or property, or event) realizes a functional type if and only if it meets the associated condition.
This is a fairly abstract definition, and it would be really great to have an example here. Melnyk gives a few:
Examples of functional object kinds plausibly include can openers, digestive systems, and cells.... Examples of functional properties plausibly include transparency, having currency, and being an analgesic.... Examples of functional event kinds plausibly include storms, births, and extinctions.(pp.21-22)
Unfortunately, he neglects to explain what the associated condition is for each of these examples. Perhaps the associated condition for being a can opener is "having the ability to open cans"?
At any rate, we can now say what it means for something to be physically realized:
A token x of functional type, F, is physically realized if and only if (i) x is realized by a token of some physical type, T, and (ii) T meets the associated condition for F solely as a logical consequence of the distribution in the world of physical tokens and the holding of physical laws. (p.23)Here, again, it would be great to have an example or two, but unfortunately Melnyk doesn't provide any. So let me try to interpret this statement.
A can opener is an object of functional type in that it is capable of opening cans when wielded by a human (with some conditions of the human's strength, size, and mental ability presumably required). Note that "can" and "human" are not definable in purely physical terms, so they are (I think) non-physical in Melnyk's view.
The type "can opener" is physically realized if there is some configuration of atoms that meets the condition of being able to open cans, and does so purely by virtue of the physical properties of the atoms of which it is composed.
The can opener is a bad example, because probably no one doubts that can openers are physically realized. Later, Melnyk gives a really interesting example: a computer program.
A computer program is about as non-physical as something can be. It's an abstract set of processes relating some inputs to some outputs. It's really a mathematical function of a particular sort, though we don't usually talk about it that way. You can, of course, write it down, or type it into your computer so that it is stored in memory, but that doesn't make the program physical any more than writing down your thoughts makes them physical.
A computer program is a great example of a functional type. A particular computer can be said to be running the program if the the physical bits of the computer act according to a certain pattern: they are "related to one another in mathematically specifiable ways." (p.40) In Melnyk's language, those mathematical specifications are the associated condition, and any computer that meets that condition is realizing the computer program.
This, I think, provides an ideal example of what physicalism is all about. It doesn't deny the existence of abstract, non-physical things such as computer programs. But it claims that all actual instances of such things are physically realized.