The word, internship, has been assimilated into Japanese language, so that there is no exact alternative for it. 実習 is kind of word for college students. For getting their degrees, they need to take practical trainings called 実習。As for 研修, it describes the term right AFTER people get employed, and they're served as apprentice during the period. So both are similar but totally different with インターンシップ. edit: It depends on the context. If the word is used for a potential employee, it means probationary period as you said. But if it used for a regular employes, then 研修 means just training program. btw, your japanese is awesome, which motivates me a lot!