堆 duī crowd

crowd; heap; pile; mass; to pile up

怎么记住“堆”: 土 earth + 隹 pigeon = crowd. A boy tosses bread crumbs onto the earth in the park, and every pigeon in town lands in one big crowd.

部件结构

堆 = 土 earth + 隹 pigeon

Gushi 故事

A boy tosses bread crumbs onto the earth in the park, and every pigeon in town lands in one big crowd.

Measure word for messy piles: 一堆问题 (yī duī wèntí) - a pile of problems, often used casually to complain about excess or clutter.
As a verb, 堆 means to pile something up: 把书堆在桌上 (bǎ shū duī zài zhuō shàng) - pile the books on the desk.
堆积 (duījī) is the more formal/written version, common in phrases like 堆积如山 (duījī rú shān) - piled up like a mountain, for a huge backlog.
The measure-word use (一堆 + noun) is very frequent in everyday spoken complaints.