Rigid flex PCB, also known as a rigid-flex PCB, is a hybrid between a rigid and a flexible PCB. This board combines rigidity, stability, flexibility and a high capacity for bending and twisting in tight or small spaces. It consists of multiple layers with flexible substrates attached to one or more rigid boards to provide greater stability. https://www.viasionpcb.com/blog/what-is-rigid-flex-pcb/