This one’s marginal to many of us, but in case you’ve seen the letters before and wondered, this one’s not too technical … at first. How FPGAs work, and why you’ll buy one.
The basic lowdown is that modern FPGA’s have “DSP slicers” in them. The important part for music:

In addition to being a hardware prototyping platform and an accelerator architecture, FPGAs are also uniquely suited for software-defined I/O…. FPGAs are the ultimate platform for software-defined I/O because of their timing control (if I said 4 cycles, it takes 4 cycles)

Somewhat related: Android’s 10 Millisecond Problem: The Android Audio Path Latency Explainer