I’m always intrigued when a kanji study guide includes “unlikely” vocabulary choices, such as today’s surprise proverb, 弱肉強食. The four characters are common and important, and taught fairly early in most books, but the combination isn’t a phrase most students will use, and one hopes that they won’t be hearing it much, either.
Loosely translated, it’s “the strong eat the weak”.
Another one that jumped out at me was 帰国子女, “children who return to Japan after living abroad”. It’s a lot more useful, especially if, like me, you were trying to figure out the meaning of the title of the light novel 彼女は帰星子女.