Wiktionary
externship
n. An experiential learning opportunity, usually offered by a school, similar to an internship, but generally shorter in duration.
Wikipedia
Externship
Externships are experiential learning opportunities, similar to internships but markedly less rigorous, provided by educational institutions to give students short practical experiences in their field of study. In medicine it may refer to a visiting physician who is not part of the regular staff. It is derived from Latin externus and from English -ship.
The term externship has a first known use date of 1945 in the Merriam-Webster dictionary.
Externships are generally shorter than internships and often last for approximately a few weeks to months.