FPGA: A field-programmable gate array, a type of Logic Chip that can be Programmed

In simple words, a field-programmable gate array (FPGA) is a a type of logic chip that can be programmed.
FPGA is an integrated circuit designed to be configured by the customer or designer after manufacturing—that is why called "field-programmable". An FPGA is similar to a PLD, but whereas PLDs are generally limited to hundreds of gates, FPGAs support thousands of gates. Once the design is set, hardwired chips are produced for faster performance. They are especially popular for prototyping integrated circuit designs.
The FPGA configuration is generally specified using a hardware description language (HDL), similar to that used for an application-specific integrated circuit (ASIC) (circuit diagrams were previously used to specify the configuration, as they were for ASICs, but this is increasingly rare).

FPGAs can be used to implement any logical function that an ASIC could perform. The ability to update the functionality after shipping, partial re-configuration of the portion of the design and the low non-recurring engineering costs relative to an ASIC design (notwithstanding the generally higher unit cost), offer advantages for many applications.
FPGAs contain programmable logic components called "logic blocks", and a hierarchy of reconfigurable interconnects that allow the blocks to be "wired together"—somewhat like many (changeable) logic gates that can be inter-wired in (many) different configurations. Logic blocks can be configured to perform complex combinational functions, or merely simple logic gates like AND and XOR. In most FPGAs, the logic blocks also include memory elements, which may be simple flip-flops or more complete blocks of memory.

Xilinx Co-Founders, Ross Freeman and Bernard Vonderschmitt, invented the first commercially viable field programmable gate array in 1985 – the XC2064. The XC2064 had programmable gates and programmable interconnects between gates, the beginnings of a new technology and market. The XC2064 boasted a mere 64 configurable logic blocks (CLBs), with two 3-input lookup tables (LUTs). More than 20 years later, Freeman was entered into the National Inventors Hall of Fame for his invention.

FPGA Market:
Xilinx is the top leader in providing high quality FPGA with 51% market, Altera is the top competitor of Xilinx With 34% market.