Radak citing Targum Yonasan: It is Germamya.

Radak: Some say that they are good fast horses. They are better than Stam horses, just like cavalry are better than Stam soldiers.

Radak: They are men who ride horses, like the simple meaning. Where they sell slaves, like blacks are sold nowadays, some are proper for slaves, and some to ride horses. Yavan, Tuval and Meshech brought "Nefesh Adam" (13) ? people proper for slaves, and Togarmah brought Parashim, proper to ride horses.

Refer to 27:12:6:1-4.

Radak: Here Yonason translates 'they bring merchandise into you.' (In verse 12, he translated 'your treasure-house.')