0.25 bitcoins is equal to 25 what?
Go to Preev.com , its a great bitcoin converter.
But useless to this conversation.
I mean the terminology. Like 1/100th of a dollar is a penny.
The OP is looking for a "name" for 0.25 bitcoin.
In the same way that 0.25 dollars is called a "quarter", 0.10 dollars is called a "dime", 0.05 dollars is called a "nickle", and 0.01 dollars is called a "penny", and any increment of pennies are called "cents".
I suppose you could call 0.50 BTC a "half-bitcoin", 0.25 BTC a "quarter-bitcoin" or a "fourth-of-a-bitcoin", 0.10 BTC a "tenth-of-a-bitcoin", 0.05 BTC a "twentieth-of-a-bitcoin", and 0.01 BTC a "hundredth-of-a-bitcoin". But other than the half-bitcoin that all feels a bit silly.
I suspect people will stick with referring to 0.25 BTC as "point twenty-five bitcoin" for quite a while. When average prices of everyday things begin all having two or more leading zeros, you *might* see people referring to values like 0.00125 BTC as "one point two five (or one and a quarter) millibitcoin" (or millibits, or millies, or millys or millis, or mils, or whatever slang develops organically), but it's quite likely that people will simply skip the millibitcoin designation and go straight to referring to the value as "twelve hundred fifty microbitcoin" (or microbits, or micros, or mikes, or mikeys, or micks, or whatever slang develops organically).