约束 (yuē shù) literally combines 约 (to bind, agree, or limit) and 束 (to tie up or restrain), forming a word that means 'constraint' or 'restriction' as a noun, and 'to constrain' or 'to restrict' as a verb. It conveys the idea of imposing limits—whether by rules, agreements, laws, or natural conditions—to control behavior or prevent excess.

This word is commonly used in formal, academic, or technical contexts—for example, discussing legal limits, ethical boundaries, ecological carrying capacity, or behavioral guidelines. In animal-related contexts, it often refers to natural or human-imposed limits on movement, population growth, or resource use (e.g., habitat constraints for wildlife). Unlike colloquial terms like 限制 (xiànzhì), 约束 carries a stronger sense of obligation, mutual agreement, or systemic limitation rather than mere prohibition.