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In the world of programming, keywords are the foundation upon which code is built. They are special words that have been reserved by the programming language itself. Each keyword has a fixed meaning and a specific function that is crucial for the language's structure. Consider them as the skeleton or the essential building blocks of a programming language. For instance, in languages like Python and Java, you will encounter keywords like if, else, for, and while. These control the flow of the program.

Keywords are standardized and uniform across any code written in the same language; they are what helps different programmers understand the structure of each other's code. An attempt to use a keyword for any other purpose such as variable naming would result in an error, as they are 'reserved' for their defined purpose. This restriction ensures the clarity and functionality of the programming language.

While keywords are predefined, programmer-defined symbols are, as the name suggests, created by the coder. These are the identifiers, such as variable names, function names, or class names, that serve as unique tags for elements within a programmer's code. They offer the flexibility needed to name entities in a way that makes sense for the specific program's context. For instance, a variable storing a user's age might be named user_age, or a function calculating total expenses might be termed calculateExpenses.

Identification rules vary between programming languages, but common conventions often include starting with a letter or underscore, and avoiding the use of spaces and special characters. Understanding and correctly using programmer-defined symbols are critical for writing clean, readable, and maintainable code.

The structure of a programming language is like a blueprint—it outlines the rules and syntax for how the code should be written and organized. Keywords, which we've discussed earlier, play a vital role in this structure, dictating how different components of the program interact with one another. Beyond keywords, structure also refers to the grammar of the language: things like where semicolons are required, how blocks of code are grouped using braces or indentation, and the way comments are incorporated to support readability.

Understanding the structure is crucial; it's akin to knowing the rules of grammar while writing a language. It ensures that the program is not only functional but also logically organized and understandable to others. Every programmer must familiarize themselves with the structure of the language they are using to ensure their code can be successfully compiled and executed.

Variable naming is somewhat of an art mixed with practical science. The names we give our variables can make our code read like a story, or like a puzzle that even the original writer struggles to put back together. When you assign a name to a variable, you are creating a readable reference to data stored in memory. These names should be both succinct and descriptive enough to communicate the intended use of the variable. For example, numApples is immediately more informative than simply num or n.

Conventions for naming variables can differ among various programming languages and project styles, but some universal recommendations include using camelCase or snake_case, avoiding conflict with keywords, and staying clear of numbers and special symbols at the beginning of the name. A well-named variable can often reduce the need for additional comments and make the code self-explanatory, which is always a goal to strive for.