Systems thinking has many definitions, but I like to think that it is simply about understanding parts, wholes and their relations. Systems thinking was developed after the second World War by numerous scholars coming from different fields, including biology, engineering and management.
I think systems thinking is easier to understand by first contrasting it to analytical thinking. Analytical problem solving begins by taking a whole into its constituent parts for further observation. For example, you would take an automobile into its parts and analyze the parts in order to understand the automobile. Using systems thinking, instead of taking the whole into parts, you would observe how the whole is connected to its surroundings. In the case of the automobile, you would try to understand the car in the context of the various transportation systems we are using today.
Systems thinking is not a discipline the same way e.g. biology or physics are, but a general way of approaching issues. It can be applied to almost any situation similar to how we use analytical thinking in problem solving. If you wish to learn more about systems thinking, I suggest you first read my post about what systems thinking is, and then read a few examples of systems thinking in order to gain further intuition.
Please do share your thoughts about systems thinking in the comments. Do you think it might be useful to you, or are you still a bit skeptical? Maybe you have been studying or practicing systems thinking and your views differ from mine? I am still a novice in this topic and I do appreciate it when someone questions my views. That way you help me learn more!