सन्धि (sandhi) means junction or joining. When two Sanskrit words are spoken together, the sounds at their border blend into the smoothest possible combination. This is not sloppy speech — it is a strict, rule-governed system that Pāṇini codified 2,500 years ago. Every sandhi change follows a predictable rule. Once you learn the rules, you can always work backwards from the blended form to the original words. Think of sandhi like two rivers meeting: where they join, the waters mix. The original rivers still exist — you just need to know the rules of how currents blend.