In Learning Systems Thinking, Diana Montalion presents the following definition of “systems thinking”:
Systems thinking is a system of foundational thinking practices that, when done together, improve nonlinear thinking skills.
Note that this is a recursive definition—systems thinking is itself a system of practices, and should thus be subject to analysis, modification, and improvement by those same practices (and in so doing, by new practices as well). This is a delightful illustration of the nonlinearity emphasized within the book.
References
Montalion, Diana. Learning Systems Thinking