'卖关子' (mài guānzi) is an idiomatic verb meaning to deliberately withhold information or delay revealing something in order to build suspense, tease, or stir curiosity—much like a storyteller pausing before the climax. Literally, '卖' means 'to sell', '关' means 'gate' or 'barrier', and '子' is a nominal suffix; together, the phrase evokes the image of 'selling a gate'—setting up an obstacle to knowledge, then charging attention (not money) for its removal.

This expression is commonly used in informal spoken Chinese, especially when someone is being playfully mysterious—like a friend hinting at big news but refusing to spill the details, or a teacher pausing before announcing exam results. It carries a lighthearted, often slightly mischievous connotation, not malice. While it can occasionally sound mildly critical (e.g., if overused), it’s generally neutral-to-positive and widely understood across age groups.