It could refer to density, where the mass is measured in milligrams and the volume in decilitres. OrIt could refer to concentration in a fluid where the mass of the "active" substance is measured in...
Mean can mean you are being rude or in math terms it is adding a set of numbers then dividing by the total amount. ex. If your numbers are 1,2,and 3 add them to get 6 and divide by 3. You get 2.
The mean distance is the same as the mean of a set of numbers,but this time, instead of them just being numbers, they're lengths. You just simply add up all the numbers and divide the total length,...