Bitstream

The file that programs the FPGA.

The bitstream is the binary output of the whole flow, synthesis, place and route, then bitstream generation, containing the configuration of every LUT, routing switch and I/O. Load it over JTAG for development, or from flash for production boot; SRAM-based FPGAs (most of them) forget it at power-off, flash-based parts (MAX 10, some Lattice) keep it.

Bitstream formats are vendor-proprietary, except where the open-source community reverse-engineered them (iCE40 and ECP5, the basis of the open yosys/nextpnr flow).