Technical reports are documents that describe the process, progress, or results of technical or scientific research. They are usually numbered report series published by university departments, companies and government agencies. They are a type of publication commonly referred to as grey literature, which is not peer-reviewed and intended for rapid dissemination of technical information before it is presented at conferences or published in scientific journals.
Technical reports can be a challenge to find because the publication and dissemination of these documents is generally not centrally coordinated by a single publisher. You may have to search in multiple databases, online indexes and websites that provide access to technical reports.