侧躺 (cè tǎng) literally combines 侧 (cè), meaning 'side' or 'to the side', and 躺 (tǎng), meaning 'to lie down'. Together, it specifically describes the physical posture of lying horizontally with the body oriented sideways—either on the left or right side—rather than on the back (仰躺) or stomach (俯卧). This term is commonly used in medical, wellness, and daily life contexts, especially when discussing sleep positions, physical therapy, postpartum recovery, or infant care.

Unlike general terms like 躺 (to lie down), 侧躺 emphasizes orientation and intentionality: it implies a deliberate, stable side-lying position often recommended for comfort, digestion, or safety (e.g., to prevent choking or acid reflux). It appears frequently in health advice, yoga instructions, and baby-care guides. The word functions as a verb and can be modified by adverbs (e.g., 安静地侧躺) or used in serial verb constructions (e.g., 翻身侧躺).