We’re not sure when this behavior changed in WhatsApp — I was able to track it down as far back as version 2.12.134 but it might have been there before — but it’s worth pointing out nonetheless, if only for its boost in convenience. It used to be that whenever you wanted to look for specific words in your WhatsApp chats, you first had to select the conversation where that word occurred and then perform the search. That was useful, but only to a limited extent, because if you were looking for that restaurant recommendation from a few months ago, you might have forgotten which friend mentioned it to you.
Now you can do an app-wide search, encompassing all of your chats. When you start a search in WhatsApp’s Chats tab, instead of only getting the names of your contacts and groups, you also get all of the instances where the term occurred in various conversations. It’s definitely handier than having to dig into each discussion separately to find what you’re looking for.