What is the difference between S&P 500 and large-cap?

Could you please elaborate on the key differences between the S&P 500 index and the large-cap category of stocks? Are they simply interchangeable terms, or do they represent distinct aspects of the stock market with specific characteristics and investment implications? How do they differ in terms of composition, market capitalization, and the types of companies they represent? Additionally, how do investors typically approach these two when constructing their portfolios, and what factors should they consider when making such decisions?