The phrase "thick waistband" refers to a wide strap or band that fits around the waist of clothing, usually to provide support or hold the garment in place. Full definition
The shirred side and thick waistband provide a tummy - smoothing and hip - concealing silhouette. (torrid.com)
Improved design: New pants have elastic at the leg cuff to better hold a rolled pant leg and a thicker waistband for ease in adjusting to slimmer babies! (mamaroobabysling.com)
These trouser leggings have a thick waistband which holds my midsection in securely (but comfortably) & the side panel ruche makes them completely appropriate to wear outside of your house. (shannonvalle.space)