Which of the following describes postures that are technically complex or difficult?

Peak postures refer to advanced yoga poses that often require a greater level of strength, flexibility, balance, and coordination. These postures are typically more challenging and may involve intricate body alignment and engagement of multiple muscle groups. The term "peak" designates these postures as the culmination of a sequence, meant to be approached after building strength and flexibility through foundation and basic postures. In practice, peak postures are frequently linked to the goal of a particular yoga session, marking them as technically complex or difficult in nature.

Basic postures serve as the starting points for practitioners and are generally more accessible, while foundation postures are the essential movements that support the development of more complex poses. Quadrant postures is not a standard term commonly used in yoga terminology. Thus, peak postures are appropriately recognized for their complexity, making them the correct choice in this context.