Daily Money is a random amount of Galleons that you can collect once (sometimes twice) a day. The amount changes every hour and you do not have to take the amount unless you want to. That means you can check back each hour until you see an amount that you would like to grab!
"Money can usually be collected once a day (not every 24 hours). However, if you are active enough, you might get an extra opportunity to collect your daily money again in the same day. If you do, you will be notified via event so keep your eyes open! Additionally, every day will have a bonus hour in which your money might be multiplied (or you might lose it all so good luck on picking the right treasure chest!)."
In December, to celebrate HEXmas and give an opportunity for users to have more money to buy presents, there is special Santa Daily Money. This can include some of the same amounts but is generally different and includes odd amounts such as 375 Galleons.
However, the main part of this is that Santa Daily Money includes much higher amounts. Where (barring the multiplier hour) normal Daily Money can go up to ~2500 Galleons, Santa Daily Money can go as high as 10,000. The multiplier hour still works in the same way, meaning that it is possible to get 40-50,000 in one go if you get a high enough multiplier.