As Aaaaaarnnold would say, "My CPU is a neural-net processor; a learning computer."
Using information garnered from your clicking of “Report spam” and “Not spam” buttons, the networks will help learn themselves what constitutes spam and what doesn’t. Google explains that the new feature will “detect and block the especially sneaky spam.”
The AI will also learn about your individual preferences, too. “While your neighbor may love weekly email newsletters, you may loathe them,” writes Google. “The spam filter can now reflect these individual preferences.”
So… one step closer to SkyNet but less spam!