1.
physical stance of readiness; defensive posture
A body posture taken in preparation for a physical confrontation, attack, or sudden movement. Used in martial arts and sports.
2.
mental readiness; bracing oneself; being on guard
A figurative stance of psychological preparedness or wariness, as when anticipating difficulty, criticism, or an uncomfortable situation.
Noun form of the verb 身構える (to take a stance; to brace oneself). From 身 (body/self) + 構える (to set up; to assume a position). The noun form refers to both the physical posture and the psychological state of readiness.
The verb form 身構える is more common in everyday use. The noun 身構え appears in descriptions of stances and attitudes.