To examine, investigate, or look into something to gather information or assess its value.
This phrase evolved from library terminology where books were 'checked out' for borrowing. By the mid-20th century, it expanded to mean any kind of investigation or examination, often with a sense of curiosity or interest.
The library origin gives this phrase a delightful sense of temporary borrowing - when you 'check something out,' you're taking a closer look with the option to return it if it doesn't interest you. It's exploration without commitment.
Complete word intelligence in one call. Free tier — 50 lookups/day.