Logs
also: log, log file, log files, server logs
A running record your app writes as it works, noting what happened and when, like a diary you can read later.
Timestamped text entries written by an application or server as it runs, usually tagged with a level such as info, warn, or error. Logs are the main way to see what happened in a system you can't watch directly.
A ship's logbook. The captain notes course changes, weather, and problems as they happen. After a storm, you read the log to piece together what went wrong.
When something breaks in production, logs are often the only evidence. Pasting the relevant log lines to your agent turns a guessing game into an investigation.
The logs show the payment notification arriving at 14:02 but no 'order saved' entry after it. The failure happens between receiving it and writing to the database.
Here are the logs from the last failed signup. Read them and tell me which step failed before you suggest any changes.
Thinking logs record everything automatically. They only contain what the code was written to log. If nobody logged a step, there's no record of it.