Gully head activity (GHA) is a critical indicator of landscape instability and soil erosion, yet existing concepts and assessment approaches remain fragmented across temporal scales and lack an explicit representation of longterm stabilization processes. This review synthesizes advances in gully morphology, topographic thresholds, gully head retreat rates, erosion susceptibility, and short-term erosional sub-processes, and identifies key conceptual and methodological gaps. Existing long-term (e.g., hypsometric analysis, threshold-based stability), midterm (retreat rate and susceptibility), and short-term (process-based and evidence-based field criteria) approaches capture complementary but partial aspects of GHA, while failing to describe the continuous transition from active development to terminal stability. To address this gap, an integrated spatiotemporal framework is introduced that couples topographic thresholds with hypsometric integrals (SSI) to jointly quantify the temporal development stage (T) and the remaining development potential (D) of gully heads. Application in China's Northeast Plain and Loess Plateau demonstrates the framework's capability to reveal stage-dependent variations in gully head activity and to distinguish developmental trajectories under different geomorphic and land-use conditions. By transforming GHA assessment from static classification toward dynamic evolutionary interpretation, this framework provides a process-oriented basis for diagnosing gully head instability, prioritizing erosion-prone locations, and tailoring management strategies to specific stages of gully development. It further offers a conceptual foundation for exploring gully responses to environmental change and for supporting targeted erosion mitigation under changing climatic and land-use conditions.