Orderby in short code

The deception page of the plug-in shows the sort code parameter:

“orderby – Sort retrieved posts by parameter. The default is none.”

If the default is none – what values can the parameter take?

I am particularly interested in sorting by a custom field – on one of my sites I am doing reviews of TV/Audio stories and wish to order the the thumbnails in order of broadcast date which I store in a custom field.

Is this possible?

Thanks

https://wordpress.org/plugins/thumbnail-grid/