I thought the English term lab was just a boiled-down version for laboratory. I think DL should not use such colloquial translations (if they even exist!), because you can't find it even in Dictionary.com. There are many synonyms for lab but none of them is course. Anyway thanks for your help!
"lab" is not really a colloquialism, and it's also not a synonym for 'course'. When you study engineering or (natural) science you have laboratory course/classes, lab for short, where you do experiments, write protocols, etc. In Germany the same classes/courses are called "Praktikum".
I agree that it is maybe a little too specific to ceratin courses of study to be known by everyone. There is the same problem in Germany: I studied physics and when I told people (who didn't study engineering/science) that I had no time because of a "Praktikum", they always thought of internships, not laboratory courses.