Tear troughs are a groove extending from the inner eye corner,  downward and outwards and causing hollowing or dark shadows under the eyes, or in severe cases, the appearance of eye bags. They create a hollow at the junction between the lower eyelid and the cheek. Often tear troughs formation are genetic 

Bags under eyes — mild swelling or puffiness under the eyes — are common as you age. With aging, the tissues around your eyes, including some of the muscles supporting your eyelids, weaken. Normal fat that helps support the eyes can then move into the lower eyelids, causing the lids to appear puffy. Fluid also may accumulate in the space below your eyes, adding to the swelling.

Dermal fillers can help to smooth the transition between the lower eyelid and the cheeks, and make the appearance of tear troughs or eye bags less obvious.