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A for loop is a control flow statement used in programming languages to execute a block of code repeatedly until a particular condition is met. The loop consists of three parts: the initialization, the condition, and the increment/decrement.

The initialization sets the starting point of the loop and is executed once at the beginning of the loop. The condition is checked at the beginning of each iteration to determine whether the loop should continue to execute or not. If the condition is true, the code inside the loop is executed, and if the condition is false, the loop terminates.

The increment/decrement occurs at the end of each iteration and updates the value of the variable used in the condition. This is important because if the variable never changes, the loop will continue to execute forever, which is known as an infinite loop.

For example, here is a basic for loop in Python that prints the numbers 0 to 4:

for i in range(5):
  print(i)

In this example, the range function generates a sequence of numbers from 0 to 4, and the loop executes once for each number in the sequence. The variable i is used as a counter to keep track of which number is being printed, and it is incremented automatically at the end of each iteration.