The High Republic Era was a period of time that lasted for around two hundred years between approximately 300BBY and 82 BBY in which the Galactic Republic was said to be at its height. It was also a golden age for the Jedi, who were significantly more active throughout the galaxy, and a time of expansion and exploration in the Outer Rim Territories.
Yoda may have uncovered a clue to one of the biggest mysteries of the High Republic right now.