What is Fidyah?
Fidyah is a religious donation to help those in need. It is only paid when someone is unable to fast during Ramadan due to medical conditions / pregnancy or any other valid reasons such as a prolonged illness, and will therefore not be able to make up for the fast. In Ramadan, the Fidya must be paid for each fast missed.
"Fast for a specific number of days, but if one of you is ill, or on a journey, on other days later. For those who can fast only with extreme difficulty, there is a way to compensate- feed a needy person. But if anyone does good of his own accord, it is better for him, and fasting is better for you, if only you knew." - Holy Quran 2:184