Discens

A discens (Latin: discens, -entis) was a soldier of the military of ancient Rome who was in training to become an immunis, or specialist within the army.

Immunes took up the trades and skills of engineers, field medics, carpenters, and craftsmen. However, they were also fully trained and would be expected to fight in the infantry or cavalry if necessary. The discentes were probably exempted, like the immunes, from standard combat and camp duties since their main occupation would have been time-consuming technical training.

Some known classes include:

...
Wikipedia