What's "built-in" mean?

Native speaker’s answer
Rebecca
"Built-in" means something similar to "inherent," and means to be already existing as a natural or characteristic part of something. So "built-in compass" here means that it is not a software update or something new to download, but a feature that is already included with the watch. Ex: The software has many useful, built-in features. Ex: The bookcase is built into the wall.