Việt Kiều means overseas Vietnamese — Vietnamese people living outside Vietnam and, often, their descendants. It is the standard term inside Vietnam, and it carries different emotional weight depending on who says it and who hears it.
The word combines Việt with kiều, a term meaning something like sojourner or resident abroad. In Vietnam it is used constantly and usually neutrally: Việt Kiều relatives, Việt Kiều remittances, Việt Kiều visiting for Tết.
Emotionally it is more complicated. It can imply relative wealth, a foreign accent, a certain way of dressing or spending. It can be affectionate. It can be a small distancing — a way of saying you're one of us, but from over there.
Abroad, reactions vary by generation. Some first-generation people use it about themselves without hesitation. Many second- and third-generation people prefer "Vietnamese American," partly because Việt Kiều frames them in relation to a country they may never have lived in.
There is no wrong answer. It is worth knowing the word, knowing that it will be used about you in Vietnam, and knowing that it is describing where you grew up rather than measuring how Vietnamese you are.
Usage and connotation vary by region, generation, and speaker. Some overseas communities embrace the term; others avoid it entirely.