堆积 is a verb meaning 'to pile up' or 'to accumulate', often implying an unplanned, gradual, or excessive buildup of things—whether physical objects (like papers, snow, or waste) or abstract elements (like problems, stress, or data). The character 堆 means 'pile' or 'heap', suggesting a visible, layered mass; 积 means 'to accumulate' or 'to gather over time', emphasizing gradual collection. Together, they form a compound that stresses both the physical arrangement and the temporal process of accumulation.

This word is commonly used in everyday contexts involving clutter, storage issues, environmental concerns (e.g., plastic waste), or even figurative situations like emotional burdens or bureaucratic delays. It carries a slightly negative connotation—suggesting disorder, inefficiency, or neglect—unless softened by context (e.g., 'snow accumulating naturally'). It’s often followed by a noun object and can appear in both active and passive constructions (e.g., '垃圾堆积' or '问题被不断堆积').