A Lab tends to vary in terms of which department you're doing it in. For chemistry or physics, it is usually to carry out some sort of experiment for a few hours in that day; for engineers again it is something practical and in the aim of producing something physical usually. In the case of MORSE, it usually refers to practical sessions in a computer lab learning how to use some piece of mathematical or statistical software. You are usually given a sheet of problems, most of which you should solve in the hour session and the rest before the next weekly session if needs be. As far as I can remember, for the two courses I have taken which have had labs, "Statistical Laboratory" and "Forecasting and Control" answers are given eventually, although the questions rarely change from year to year. These Labs were technically not compulsary when I did (or rather didn't do) them, though things may have changed. As you might guess, other modules to do with programming often have labs.