Fpga is field programmable gate arays so basicly gpus that are just for numerical applications use much let power and emit less heat have thr same power as a gpu at a fraction of the power cost, asic is aplication specific intergtrated circuit these use large amount of ddr5 and are simalry whist very different to a gpu these can only be used to mine but mine are a higher rate with low power consunption
Eg, 1 amd 7950 mines at 750khs using 200w costing £200 to buy
1 fgpa will mine at 750 khs using 20w of electroc and can be connected using usb allowing alot of fgpas to be run on single pc cost could be around 500-700
1 asic mine will mine at 75000 khs using 200w of elec using usb at a cost of around £2500 this all all estimated based on what happened to bitcoin wheb fgpa and asic first were developed