'乖乖' is a reduplicated form of the adjective '乖' (guāi), meaning 'well-behaved', 'obedient', or 'cute'. The reduplication softens and intensifies the meaning, turning it into an adverbial expression that conveys gentle compliance, endearing submission, or charming innocence. It’s commonly used in affectionate, nurturing, or playful contexts — especially when addressing children, pets, or loved ones — to encourage calm behavior or express fondness.

The term carries warm, intimate connotations and is rarely used formally or critically; instead, it evokes tenderness, reassurance, or lighthearted coaxing. While '乖' alone can be neutral or even slightly admonishing ('Be good!'), '乖乖' almost always sounds soothing and encouraging, like a parent whispering to a fussy toddler or petting a calm cat. It frequently appears in imperatives ('乖乖坐好') or descriptive phrases ('乖乖地睡觉'), often paired with verbs indicating stillness, patience, or cooperation.