This option, if available, allows you to choose what port or type of connection will be used to communicate with the braille display you have selected.
It is a combo box containing the possible choices for your braille display.
By default, NVDA employes automatic port detection, which means the connection with the braille device will be established automatically by scanning for available USB and bluetooth devices on your system.
However, for some braille displays, you may be able to explicitly choose whatport should be used.
Common options are "Automatic" (which tells NVDA to employ the default automatic port selection procedure), "USB", "Bluetooth" and legacy serial communication ports if your braille display supports this type of communication.
This option won't be available if your braille display only supports automatic port detection.
You may consult the documentation for your braille display in the section Braille Displays #SupportedBrailleDisplays to check for more details on the supported types of communication and available ports.
nishimoto 
Screen Reader NVDA Japanese
Fork
本家 main 5680 に、点字ディスプレイドライバのポート選択機能がマージされました。
日本語版の KGS ドライバには「ポート手動選択」というバリエーション (KGS2) がありますが、現在の KGS ドライバを本家の仕様にあわせたいと思います。
現状では main 5680 を日本語版にマージすると「ポート選択」のコンボボックスが２つ出てきます。
本家のコンボボックスの選択肢には、「自動」「USB」「ブルートゥース」に加えて、有効なシリアルポート番号が出てくるようです。
ユーザーガイドの Ports の項目は下記のように説明されています。
This option, if available, allows you to choose what port or type of connection will be used to communicate with the braille display you have selected. It is a combo box containing the possible choices for your braille display.
By default, NVDA employes automatic port detection, which means the connection with the braille device will be established automatically by scanning for available USB and bluetooth devices on your system. However, for some braille displays, you may be able to explicitly choose whatport should be used. Common options are "Automatic" (which tells NVDA to employ the default automatic port selection procedure), "USB", "Bluetooth" and legacy serial communication ports if your braille display supports this type of communication.
This option won't be available if your braille display only supports automatic port detection.
You may consult the documentation for your braille display in the section Braille Displays #SupportedBrailleDisplays to check for more details on the supported types of communication and available ports.