If a company uses a just-in-time system (often written JIT), it makes or buys goods only a little before they are needed, so it does not keep big piles of things in a store room. The idea is: the parts arrive, the workers use them, and the finished thing goes out — without sitting around for weeks. Though actually, it is clever when everything runs smoothly, and painful when a ship is late or a factory stops, because there is no spare pile to fall back on. People also stretch the same phrase in computing: a just-in-time compiler writes machine code at the last moment, when the program needs it, rather than doing all of that work in advance. In everyday English, just in time (no little lines between the words) simply means “almost too late, but we made it.” The little lines mark the factory idea as a set term.