The expression "i=5" is a simple assignment statement commonly used in programming and mathematics. Here, the variable i is being assigned the value of 5. This means that whenever i is referenced in the code or equation, it will represent the number 5. In programming languages like Python or Java, this assignment allows developers to store and manipulate data. For example, if you later add 2 to i, the new value of i would be 7. This concept is fundamental in computer science, as it enables the creation of dynamic and flexible programs.