In Britain, the CSA was a government office that dealt with child support: when parents no longer lived together, it could decide how much money one parent — often the father — should pay to help raise the children, and it could chase that money. People talked about "paying CSA" or "the CSA coming after him" in everyday speech, not only in law offices. It is a British public-life abbreviation, the kind you meet in newspapers, soaps, and family stories, not a science term. Though actually, that office later changed its name (the work moved to what is now called the Child Maintenance Service), but plenty of people still say CSA out of habit, the way we keep old names for buildings. Taiwan has the idea of 扶養費, but not this British office, and not this abbreviation.