What does denier mean in tights?

Glittery 50 denier tights - Black - Zizzifashion

Fiore Patterned 40 Denier Tights Morning Melange Semi Opaque Tights New

Denier tights guide: What denier means and how each number looks

What are stockings with the line up the back called? - Quora

What's A Denier – VienneMilano

Buy Black 40 Denier Opaque Tights Three Pack from the Next UK online shop

2-pack tights in 60 denier - Black - Zizzifashion

LECHERY Matte Silk Opaque Tights 1-Pair

Denier tights guide: What denier means and how each number looks