Border gore means: Political borders which appear extremely messy and unaesthetic when viewed on a map, typically due to being extremely jagged or involving many enclaves.. It is informal slang, fine in casual speech but not suited to formal contexts. There is no real cause for parental concern; it is descriptive vocabulary rather than risky behaviour. If your teen uses it, context will usually make the intent clear. A short, curious question about where they heard it is usually all that is needed to know whether to follow up.