An error due to the presence of undefined word(s) in the codes.
######Example 1
| Error Message |  |
|---|---|
| Bug example ✘ | Source of error: a typographical error  |
| Correction ✔ | Solution: replace the typo with the correct spelling  |
######Example 2 | Error Message | 
| | --- | --- | | Bug example ✘ | Source of error: items created in a [For loop](../chapter_3_procedures/Loops.md) cannot be [referenced](../chapter_3_procedures/Rules.md) outside of the loop.
| | Correction ✔ | Solution: define the items outside of the For loop by adding them into an external [list](../chapter_3_procedures/List.md).
|