Tofu is the soft white food made by curdling soya milk and pressing it into blocks — what you already know as 豆腐. In English it is an uncountable noun, so people say some tofu, a piece of tofu, a block of tofu, and almost never two tofus. It comes in kinds: silken (very soft, wobbly), firm and extra-firm (good for frying), and English speakers use those words on the package. In Western cooking tofu is mostly thought of as a meat substitute, something vegetarians eat instead of chicken, and that idea sits inside the word for many English speakers in a way it does not for us — for us it is just food. Because of that, tofu sometimes gets used as a joke word for something soft, pale, and boring; if someone says a film was tofu, they mean it had no flavour. That use is casual and not common. The word arrived in English through Japanese, which is why we say TOH-foo and not the Mandarin sounds.