So-called is a word we put before a name or label to show doubt, disagreement, or irony about whether that name really fits. When you say someone is a so-called expert, you're suggesting they might not actually be an expert at all. When you mention a so-called friend, you're hinting that this person isn't acting like a true friend should.

Sometimes so-called simply means “commonly known as” without any judgment, like “the so-called New World” for the Americas. But more often, it carries a skeptical tone. If your sister claims to be sick but you see her playing video games, you might mention her so-called illness. If someone brags about their so-called brilliant plan that obviously won't work, the phrase signals your doubt before you even explain why.

The word acts like verbal quotation marks, making you step back and question whether the label is accurate. It's a compact way to express suspicion: instead of saying “this person who claims to be an expert but probably isn't,” you can just say a so-called expert. The phrase warns your listener not to take the label at face value.