What does satisfactory completion of Master's degree mean?
Satisfactory completion means that you've completed the program by satisfying the requirements, as opposed to, say, simply leaving.  Additionally it implies meeting any final evaluation criteria, e.g. passing any final exams.

Usually this phrase doesn't imply anything more by itself, though it's not uncommon for additional constraints to be attached to it.  For example, if they want your GPA to be above a certain point, they may say "satisfactory completion with a GPA of at least 3.5".