Answer: Function.
Answer analysis: In programming and computer science, a function is a set of instructions within a program with a clear beginning and end.
Functions are organized, reusable blocks of code that implement single or related functions. They allow programmers to break down complex programs into smaller, more manageable parts, thereby improving the readability, maintainability, and reusability of the code.
The characteristics of functions include:
1. Encapsulation: A function encapsulates a set of related operations and only provides an interface (i.e., function name, parameter list, and return value type) to the outside, hiding the internal implementation details.
2. Reusability: Once a function is defined, it can be called multiple times in a program without having to write the same code repeatedly.
3. Parameterization: A function can accept parameters, which are provided when the function is called, allowing the function to process different data or perform different operations.
4. Return value: A function can return a value to the caller, which can be a calculation result, a status code, or any other type of data.
5. Scope: Variables defined inside a function (local variables) are visible and valid only inside the function, which helps avoid variable name conflicts and improves the modularity of the program.
In most programming languages, the definition of a function usually includes the following parts:
* Function declaration: specifies the name of the function, the parameter list (including the type and number of parameters), and the type of the return value (in some languages, if the function does not return any value, the return type may not need to be specified).
* Function body: contains the code block that implements the function. The function body starts and ends with a pair of curly braces `{}` (in some languages, other symbols may be used), which contains all the instructions required to execute the function.
Therefore, it can be said that a function is a set of instructions within a program with a clear start and end.