Multiple realities
(covers information from several alternate timelines)

Prod was a Romulan title. Nero held this title while in command of the Narada, in addition to that of captain.

In 2258 of the alternate reality, during the Narada's attack on Vulcan, Ayel addressed Nero as "prod" when informing him that seven Federation starships were on their way to help the planet. (Star Trek)

The scene in which Ayel uses the term prod was originally shot as a different scene which was ultimately deleted from the final cut. Originally, the Narada, having been damaged by the collision with the USS Kelvin, drifted into Klingon territory and was quickly surrounded by Klingon Warbirds. The scene had the Romulans speaking their native language, with English subtitles added for the audience. Speaking Romulan, Ayel addresses Nero as "prod Nero", informs him of the situation, and asks for his orders. While most of the scene was cut, the part with Ayel was maintained, but it was moved to a later point in the film and redubbed in post-production. Ayel's addressing Nero as prod remains intact, although the remainder of the scene is now in English rather than Romulan.
According to the film's script and the subtitles created for the deleted scene (the latter of which can be found on the Star Trek 2-Disc Digital Copy Special Edition DVD), prod is the Romulan term for "commander." [1] However, according to writers Alex Kurtzman and Roberto Orci in the audio commentary for the film, it was intended to mean "praetor." This is explained in the comic Star Trek: Countdown, because Nero took his teral'n from the praetor who allowed Romulus to be destroyed.