背(bèi) - back (of the body); to recite from memory in Mandarin

背 (bèi) is the back: the part of your body that aches after a long flight, the back of a chair, the reverse side of a card. From the idea of turning your back come the verb senses of facing away (背对着) and of going against someone (背叛, to betray).

The reciting sense surprises learners. 背 also means to learn something by heart and say it back without looking, which is how Chinese schools have taught texts for centuries: 背课文, 背单词, 背电话号码. It is memorising and reproducing, not merely remembering, so 记住 and 背 are not interchangeable.

The real trap is the second reading. With a first tone, 背 (bēi) means to carry something on your back: 背书包 is to wear a schoolbag, 背孩子 is to give a child a piggyback. Same character, different word, different tone, and only context and the tone mark keep them apart.