migration 是移民 (同時表示包括移出和移入居民）比如我太太移民到美國，對台灣人來說她是經過 emigration (emigrant)，對美國人來說她是 immigration (immigrant)。對台灣人和美國人，她都是 migration (migrant)。而對在台灣的我是…celebration (jk!)。
1. Emigration and immigration are both forms of migration.
2. If you move out of a country, you have emigrated, and you are an emigrant.
3. If you move into a country, you have immigrated, and you are now an immigrant.
4. Either way, or even if you move within the same country, you have migrated, and you are a migrant.
5. Also, animals and people can all migrate, but only people can immigrate and emigrate.
6. HOW TO REMEMBER
You may be familiar with the prefix ex- meaning “out” from words like exodus. If you can remember both that and identify the immigration with the word in, then this will help you to remember that emigration is from the point of view of coming out, while immigration is from the point of view of coming in.
Detailed explanation: http://www.educationbug.org/a/immigration-vs-emigration.html