What is the meaning of the Hadith: "Protect yourselves from the Fire, even if with half a date," and specifically "half a date"?

The meaning of "half a date" (شِق تمرة) is its half, and it is an exaggeration of scarcity. The intention is that the Hadith encourages doing all good deeds, whether few or many, even if it is with a kind word, and that doing so protects its doer from the Fire. One should not belittle any charity, no matter how small, for a little of it shields the one who gives charity from the Fire.