Glioma is the most common intracranial primary malignant tumor, accounting for approximately 50% of all primary malignant tumors in the brain [1]. Maximal resection is still the main therapeutic approach for glioma patients [2]. Accumulating studies have demonstrated that the extent of resection is significantly related to the prognosis of glioma patients [3–5]. However, inevitable recurrence almost occurs in glioma patients after surgery, which is closely related to residual tumors. One of the significant causes of residual tumors is the infiltrative growth pattern of glioma, which results in an unclear boundary between the tumor and the surrounding tissue. Currently, the definition of the boundary between glioma and normal brain tissue remains unclear. The main methods for delineating this boundary include pathology, imaging, metabolism, ultrasound, electrophysiology, and fluorescence. Thus, we would like to summarize the relevant research progression regarding the boundary of glioma in the past.