Immigration is permanent residence. You can move somewhere not permanently, like on a temporary work visa - that is an expat. US/UK/Canada have a lot of treaty agreements with other countries, so a Canadian citizenship will essentially allow you into many countries more easily than those coming from a third world country. People from third world countries have to go through a more intensive visa process for temporary residence.
Another reason expat applies generally is because generally an expat from the US does not renounce their US citizenship despite the tax implications due to the need/desire to return home. The US is one of the few countries that will tax a US citizen anywhere in the world, which I think leads to the increased use of the word expat.
Immigration is permanent residence. You can move somewhere not permanently, like on a temporary work visa - that is an expat. US/UK/Canada have a lot of treaty agreements with other countries, so a Canadian citizenship will essentially allow you into many countries more easily than those coming from a third world country. People from third world countries have to go through a more intensive visa process for temporary residence.
Another reason expat applies generally is because generally an expat from the US does not renounce their US citizenship despite the tax implications due to the need/desire to return home. The US is one of the few countries that will tax a US citizen anywhere in the world, which I think leads to the increased use of the word expat.