To describe an extremely large and dense crowd, so many people that they seem to fill up mountains and seas; jam-packed with people.
今天商场里举行促销活动，真是人山人海，顾客们挨山塞海地挤在一起，想买到心仪的商品。
Today, there's a promotional event at the mall, it was truly a vast crowd, with customers packed shoulder to shoulder, trying to buy their desired items.
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