See also: Measure | Forward Error Correction
An error is a system mistake or incorrect result, eg. a bug. Errors may need troubleshooting to fix a problem. A computers performance is measured by how error prone it is.
Errors can arise from false information, compatibility and configuration issues, as well as corruption of data, poorly written code, buffer overflow exploits, etc.
Quality control, Redundancy, audits and other security measures can help alleviate errors. Severe errors may develop into downtime.