"ConventionEngine" is a collection of Yara rules looking for PEs with PDB paths that have unique, unusual, or overtly malicious-looking keywords, terms, or other features. For further reading on the context, please see the @FireEye blog series on the subject.

https://www.fireeye.com/blog/threat-research/2019/08/definitive-dossier-of-devilish-debug-details-part-one-pdb-paths-malware.html

Keywords = string words used by malware developers to organize files, folders and code projects, often describing the functionality of the malware.

Terms = string words that show up in paths as a result of operating system, software, or user behavior, often indicating that the developer is riding solo or that code project is not being developed for a "enterprise" software product.

Anomalies = Other things that are less common but are suspicious or indicative of various behaviors.

See also here: https://www.fireeye.com/content/dam/fireeye-www/blog/pdfs/definitive_dossier_pdb_yara_appendix.pdf