As a Russian you are maybe not familiar with the concept of "limbo" which comes from western theology. As far as I know this concept does not exist in orthodox theology. It is a state of afterlife between heaven and hell (and distinct from the purgatory) where unbaptized childred and people who died before Christ lived dwell. There was an argument in catholic theology whether this state be permanent or transitory. Hence there is an element of suspense connected with this concept.
In English you use the expression in limbo when you would not know if you will live or die (e.g. a person sentenced to death who is waiting for this appeal to be decided). In a further generalization it means that you are in an uncertain situation as to your future. As a postgraduate student you are often in a awkward state of suspense concerning you career.