Revenue Per Available Night (or RevPAR) gives you a snapshot of how well your listing is booking and for how much by incorporating your revenue and occupancy for a given month.
To calculate the Revenue Per Available Night, you would take the total revenue in a time-frame divided by number of bookable nights in the time-frame. Equals ADR * Adjusted Occupancy.
Your listing earned $3,000 last month and you only had 25 days available.
$3000 / 25 days = $120 per day is your RevPAR.