Precursors were ancient alien species that existed before the modern era in the Vanaad Galaxy. While the specific name for them can vary by race, the most common term is Precursor. Any sapient species which existed before the modern era and is no longer around in a notable fashion beyond relics can be considered a Precursor. Little is known about most Precursors, beyond a few basic things that have been gleaned from the artifacts they leave behind.
In the galaxy today, relics left by Precursor species can be found in many places. Some of these relics are more intact and advanced than others, while some are but useless husks worn away by time. Many technologies are able to be reverse-engineered from the relics, and so they are incredibly valuable to those who find them. The discovery of a Precursor datacache, for instance, can propel a species forward hundreds of years.