What is a template in C++?

In C++, a template is a powerful feature used to create functions and classes that can operate with any data type. This allows programmers to write a function or class definition once and then use it with different types. When you define a template, you can specify placeholder types instead of concrete types, which C++ will substitute with actual data types when the template is instantiated.

For example, with function templates, you can write a single function to sort an array of any data type (like integers, floats, or even user-defined classes) without the need to overload the function for each type. This brings about flexibility and reusability in code.

The other options do not accurately describe templates. A standard library function is a built-in function provided in C++ libraries, while defining constants relates more to the const keyword or macros. Error handling typically involves exception handling mechanisms, not templates. Thus, the emphasis on generic types encapsulates the essence of what templates achieve in C++.