As we think about the timescale of humans, the Great Filter is one of the terms that we're using to help us understand the timescale of our future as well as our past.
The term comes to us from the discourse of physics. The Great Filter is one explanation for the Fermi Paradox. Fermi observed that our galaxy has been around long enough for extraterrestrial civilizations to have emerged and spread, but we see no signs of any other intelligent species. Where are they?
The Great Filter argument says that since we don't see a wide range of intelligent life, there must be some filtering process--a series of difficult, improbable, or impossible steps that intelligent life must evolve through. If we map the steps that we believe have led from the first star to the present existence of tool-using humans, we might well conclude that either we (aparently alone) have made it through the Great Filter, having survived a challenge that no other civilization has been able to survive. In this case, our future looks good.
If that's not the case, then the next step in our evolution is likely to be the "impossible" step, through which no other civilizations equivalent to ours has passed. In this case, our future is dim.
Once a rather arcane philosophical debate, the GEAS report has given the concept of the Great Filter more public attention.