What is the scientific name for alien?

If you are referring to the taxonomic classification of an organism not of Earth, there is no specific name for all organisms not originating from Earth, just as there is no specific name for all organisms originating from Earth. There are, as of yet, no confirmed organisms from other planets*, so none have yet been given nomenclatures.

If you are asking for a more technical term or definition for alien, the Merriam-Webster Unabridged Dictionary defines alien as:

1. 1. adj a. Belonging or relating to another person, place, or thing: strange. b. Relating, belonging, or owing allegiance to Another Country or government: foreign. 2. adjDiffering in nature or character typically to the point of incompatibility. 1. 1. noun A person of another family, race, or nationality. 2. noun A foreign-born resident who has not been naturalized, and is still a subject or citizen of a foreign country; broadly: a foreign-born citizen. 3. noun An extraterrestrial. 3. 1. verb Alienate, estrange. 2. verb To make over (as property).