Packages can be exported and imported via both the user interface ("UI") and the command line interface ("CLI"). 

Exports

• Packages exported via the command line interface (CLI) are exported as individual files
• Packages exported via the user interface (UI) are exported as a *.tar.gz archive. A package archive that was exported via the UI will contain individual files identical to a package exported via the CLI.

Imports

• Imports using the user interface (UI) require package files to be compressed into a single archive. Supported formats are “tar.gz”, “tgz” and  “tar.bz2”.
• Imports using the Drush CLI tool expect a package directory to contain individual files. Importing from *.tar.gz file via Drush CLI tools is not supported.

User interface vs command line interface