Refers to the sweet potato (Ipomoea batatas); the name associates it with the Ryukyu Islands. In modern Japanese, サツマイモ is far more common.
See also: さつま芋
Ryukyu-imo was also called kansho in the past.
Rarely used for the common potato (Solanum tuberosum); ジャガイモ is the standard modern term. This usage may appear in historical or regional contexts.
See also: じゃがいも
In some old documents, Ryukyu-imo can refer to the potato.