Final answer:
A T Tauri star is a young and evolving pre-main-sequence star exhibiting irregular variability in brightness, with strong stellar winds and material ejection.
Step-by-step explanation:
A T Tauri star is a young, pre-main-sequence star that is in the process of gravitational contraction before becoming a main-sequence star like our Sun. These stars are characterized by their erratic changes in brightness and are often associated with stellar wind and material ejection that can lead to Herbig-Haro objects. T Tauri stars are found only among stars with masses less than or similar to that of the Sun, as more massive stars do not pass through this stage according to current stellar evolution models.