1. Transient ischemic attack (TIA): (1) Time-based definition: TIA is a sudden focal neurological deficit (brain, spinal cord or retina) of <24h duration due to vascular causes. (2) Histology-based definition: TIA is a transient neurological deficit caused by ischemia of the brain, spinal cord or retina, without acute infarction. In 2010, Stroke published six definitions of light stroke and the relationship between clinical outcome to explore the best definition of light stroke. The study enrolled 760 consecutive patients with acute ischemic stroke, divided into 6 groups according to the following definitions: A. NIHSS must be 0 or l for each item and 0 for each item of consciousness; B. Luminal-like syndrome (small vessel occlusion); C. Motor impairment only (including dysarthria or ataxia); with or without sensory impairment; D. lowest baseline NIHSS score for each item (total score ≤9). No aphasia, neglect, or any impairment in level of consciousness; E. Baseline NIHSS score lowest score per item, total score ≤9; F. Baseline NIHSS ≤3; Good short-term regression defined as patient discharged home; Good intermediate regression defined as modified Rankin Scale score ≤2 at 3 months. Patients with definition A and definition F had the best short- and intermediate-term regression (74% and 90% for definition A and 71% and 90% for definition F, respectively). Patients with anterior circulation stroke with definition C were more likely to be discharged compared with patients with posterior circulation stroke (P=0.021). Older patients with definition E had poorer midterm regression compared with younger patients (P=0.001), whereas patients with definitions A, D, and F did not have different regressions in any subgroup. The currently used definition of ischemic mild stroke: a sudden focal mild neurological deficit of vascular origin (defined as NIHSS ≤3 points) of ≥24h duration or neurological deficit due to an ischemic infarct associated with clinical symptoms by imaging rather than by a cerebral hemorrhage detected by imaging.