Dose is the amount of coffee for a drink or brew, most commonly by weight in grams (g).
For example, a standard cup of drop coffee might have a dose of around 15g of medium ground coffee beans (e.g., if brewed at the standard 60g/L), and a standard double shot of espresso would tend to have 16-20g of finely ground coffee.
Dose is also a brew parameter, or variable in coffee extraction. Varying dose without changing amount of water would also change the brew ratio (another brew parameter), and would change the resistance in an espresso puck thereby also impacting shot speed.