I dont know if small em is taking an exam or looking at the practical side.. .The above answers are obviously all very technically correct. The real problem is the application of all this theory.. .From a tech log point of view I have seen 'compressor stall' and 'compressor surge' all reported for very similar problems. The reports contain references to popping, banging, vibration, indication fluctions, etc.. .From a maintenance point of view they are one of two things, either a transient that cannot be repeated in which case it is an inspection for compressor damage or mechanical failure of bleed valves or VIGV's.. .I have heard 727 stalling/surging as they go by and yet the crew did not hear anything!. .Most manuals particularly big fans, warns against high power in crosswind situation and very often, on ground runs, just turning the aircraft a few degrees clears the problem. .Again the condition of the engine has a great effect on these situations and tired or dirty engines suffer more.