Luis's response is concise an complete. A minor feedback loop involves only a single level, a major two or more levels. The distinction is important because a minor negative can only converge (never oscillate) and a minor positive loop can only grow at an ever increasing rate. Once you add another level, things change. Thus the major loop Mohammad refers to involving inventory and workforce (two levels).
Of course, one always has to be on the lookout for secondary loops, even within a minor feedback loop. One of my favorite pedagogical examples is the sales force, sales, revenue, budget to sales, sales force positive loop. You can formulate this with one level (sales force) and still get collapse if the price is too high, the sales people too ineffective, or their budget allocation too small. The reason this is true is that the workforce adjustment process is itself a negative loop. Thus, when the two combine you don't necessarily get growth.
One other thing to note is that if you use difference equations, a minor negative loop can display expanding oscillations. This can manifest in models when you have adjustment times smaller that the computational interval and use Euler integration and it can be confusing.
Not nearly as concise as Luis - but I hope that is helpful.