Someone moving from a wealthy country to a poorer one is an expat. Someone moving from a poor country to a wealthier one is an immigrant if they intend to stay

Someone moving from a wealthy country to a poorer one is an expat. Someone moving from a poor country to a wealthier one is an immigrant if they intend to stay for life, and a migrant if they don't. That's why you have American expats living in Thailand and Mexico, but Thai immigrants and Mexican migrants living in America.