A hem on something such as a piece of clothing is an edge that is folded over and stitched down to prevent threads coming loose. The hem of a skirt or dress is the bottom edge. She lifted the hem of her dress and brushed her knees.
How do you put a hem on a shirt?
https://www.youtube.com/watch?v=wJFBvZvScrk
What is hem fabric?
A hem in sewing is a garment finishing method, where the edge of a piece of cloth is folded and sewn to prevent unravelling of the fabric and to adjust the length of the piece in garments, such as at the end of the sleeve or the bottom of the garment.