As a software developer and hobbyist pedant, I don't think you're going to find a word which encapsulates all of the intended meaning while also being unambiguously understood by the listener.
In search of an applicable word, people often forget that the listener should be able to understand the word without consulting a dictionary. You usually want to be accurate specifically to avoid an unnecessarily long explanation; but using a sufficiently complicated or unknown word achieves quite the opposite.
There are ways to communicate this with a specific phrasing, rather than looking for the most applicable word.
Your description is a bit generalized and vague, so let me use a more apt example: substrings.
For non-programmer readers:
A substring is part of a piece of text (which is called a "string [of characters]"). I.e. given the string "Hello world", these are all possible substrings: "Hello", "o wor", "ld", "Hello wor", but also "Hello world" itself (which is why it's an applicable example for OP's question).
How would I describe this?
A substring is a subset [of the characters] of a string. The list of possible substrings also includes the complete string. In other words, a string is also one of its own substrings.
A slice of a data structure is a subset of [the data in] that data structure. The list of possible slices also includes the full data structure. In other words, a data structure is also one of its own slices.
In all honesty, I find it slightly harder to understand when generalized, simply because it's less clear what we're talking about. In the substring example, it's much easier to understand.
But I am assuming that you used "data structure" in your question because you were trying to generalize your question; and that you in reality will use a more concrete name instead of just "data structure".