What is a variable in programming and uses code example

Example: in coding why one variable define another

% In Matlab, Arrays start at index 1               % In Matlab, Arrays are indexed using parentheses ()               % Thus in Matlab:                              quiz_grades(1) = 98;               average_quiz_score =  ( quiz_grade(1) + quiz_grade(2) +  quiz_grade(3) ) / 3.0;