If "IN" signifies a specific cryptocurrency, like a hypothetical "Incoin," then "$BTC/IN" would represent the exchange rate between Bitcoin (BTC) and Incoin. This is a crypto-to-crypto trading pair, common on exchanges.

However, if "IN" is used informally to mean "in terms of" or "against," as in "$BTC IN USD" or "$BTC IN INR," it means the price of Bitcoin expressed in that fiat currency (U.S. Dollars or Indian Rupees, respectively). In this context, "$BTC IN" usually points to the value of Bitcoin against a national currency on a cryptocurrency exchange.