What stitch is this?

[Abs18]

https://www.instagram.com/p/CBaP5a7pvYJ/?utm_medium=copy_link

Looking to crochet a similar stitch, is this a half double crochet? Any help is appreciated! 🇨🇨

[Granny Square]

It looks like US DC to me.  The part at the top edge of the bottom piece looks like standard open filet (like for doilies), which would be *DC, ch2, repeat.  Also from the scale of the stitches, it looks like it was done in #10 doily thread, which is not too unusual for swim suits.

[Abs18]

Oooh thank you so much for your answer!! That's super useful! 😊