How data is organized, represented in programs. The difference of DataStructures used in programs may be significant in run-time performance, memory usage. These patterns are useful in their own right, but in modern systems they are usually implemented by vendor-supplied libraries and runtimes. CeePlusPlus programmers should usually use the container classes of the StandardTemplateLibrary, for example. A reasonable theoretical understanding is still required to understand the applications and trade-offs of each data structure, even though you're unlikely to implement one yourself in production code.
Includes (in order from simple to complex)
Record, Struct (optimized associative structure with fixed set of keys and often with type constraints). These aren't often considered data structures by people, as in many languages they have different syntax to access (foo.bar vs foo["bar"] in C++), but they are.
HashTable (common and efficient implementation of associative data structures if you do not care about ordered-traversal; otherwise a BalancedTree is typically used UnderTheHood? instead; usually has only one value per key)