The INSTR function is a fundamental string function in SQL. It allows you to locate the starting position of a specified substring within a larger string. This is incredibly useful for tasks like finding specific keywords in text fields, extracting parts of strings, or performing conditional filtering. It's available in many SQL dialects, including MySQL, PostgreSQL, SQL Server, and Oracle. The function's syntax is generally consistent across these dialects, making it easy to learn and apply. Understanding INSTR is essential for anyone working with text data in a database. It's a core component of data manipulation and analysis, enabling you to extract valuable insights from your data.