The structure indicated is the infraspinous fossa of the scapula.
It is called the infraspinous fossa because it lies below (infra) the spine of the scapula (-spinous). Accordingly, the fossa that lies superior to the spine of the scapula is the supraspinous fossa.
The scapula consists of two surfaces – the costal surface and the posterior surface. The infraspinous fossa is significantly larger than the supraspinous fossa and comprises the majority of the posterior surface of the scapula.
The infraspinatus muscle, one of the rotator cuff muscles, originates in the infraspinous fossa.