FPGA is an acronym for Field Programmable Gate Array. An FPGA is an integrated circuit which can be reconfigured using software tools.
FPGAs contain logic blocks, interconnects, and I/O.
Xilinx and Intel (after acquiring Altera) are the biggest manufacturers of FPGAs.
CPUs and GPUs are not reconfigurable and function based on software.
Historically FPGAs were first configured using schematic capture, then with hardware description languages such as VHDL and Verliog, and now with high level synthesis tools such as LabVIEW FPGA, HDL Coder, Catapult, etc. The next generation of tools may be overlays.
FPGAs have evolved from being having logic blocks which are homogeneous, to having more specialized components such as math focused DSP blocks. Other specialized components include microprocessors and bus interfaces. In this sense, FPGAs are converging into System on Chip (SoC).