In which two directories are third-party modules located by default?

By default, third-party modules are located in vendor/ or app/code/ directories. The vendor/ directory contains modules that are installed using Composer, while the app/code/ directory contains modules that are manually copied or cloned from a repository.

Third-party modules in Magento 2 are typically located in two directories by default: thevendor/directory and theapp/code/directory. Thevendor/directory is used for modules that are installed via Composer, Magento's dependency manager, which includes both Magento's core modules and third-party modules. Theapp/code/directory is used for custom modules developed specifically for the project or for third-party modules that are manually installed without Composer. These conventions provide a structured approach to managing Magento modules, whether they are part of Magento's core functionality, contributed by the community, or developed for specific projects​​.