When we say that there is an "implied condition" in a situation, it means that there is something that we don't say out loud, but we still expect it to happen or be true.
For example, if we borrow a book from the library, we don't say out loud that we will return it on time. But there is an implied condition that we will do so, because that's what people are supposed to do when they borrow something.
Another example is when we say "I'll meet you at the park at 3 PM." It is implied that we mean today and not tomorrow, because we didn't say "today" out loud, but we both understand that's what we meant.
Implied conditions are like secret rules that we all know and follow without even saying them out loud. They help us communicate with each other without having to explain every little detail.