It is possible to specify that statements are to be repeated. Say that you would like to print a hello message to a list of persons. You could specify:

      print "Hi Isabel, what a nice day isn't it?"
      print "Hi Kate,  what a nice day isn't it?"
      print "Hi Michael, what a nice day isn't it?"
    

A nice feature is the for control statement, that enables to specify that a statement (or a more complex sequence of statements) is to be repeated over a set of values:

      for person in ['Isabel', 'Kate', 'Michael']:
         print "Hi ", person
         print ", what a nice day isn't it?"
    

Each value of the set is assigned one after the other to a variable, here the person variable. Such a construct is generally called a loop, and the variable person is therefore called the loop variable. Notice the indented block of statements below the for. This block corresponds to the statements that will be repeated over the set of values.