An acronym is a word or name formed as an abbreviation from the initial components in a phrase or a word, usually individual letters (as in NATO or laser) and sometimes syllables (as in Benelux). There are no universal standards of the multiple names for such abbreviations and of their orthographic styling.
Son and daughter of your siblings and siblings-in-law. As with uncle and aunt, they're not your nieces and nephews by marriage, they're your nieces and nephews, plain and simple, even if they're your spouse's siblings' kids and don't have a single drop of blood in common with you.
But back to the difference between first cousins once removed and second cousins. Thatâs where Hermione helps us out, as a short while later she has a new baby son, Charlie: Alice and Charlie belong to the same generation: as children of first cousins, they are second cousins.