BODMAS is an acronym (abbreviation) to remember the order of mathematical operations.
The full form of BODMAS parts "brackets, orders, division, multiplication, addition, subtraction"
An example would be 8 + 2 * 5. You might look at this equation and come to the answer of 50. However, excel would return an answer of 18. This difference is that because of the BODMAS model excel will run the equation this way 2 * 5 + 8. Where there is a * (multiplication) or a / (division) coming after a + (plus) or - (minus) Excel will always use the BODMAS model and reverse this equation.