Flash codes are a series of light “blips” using one or two lights. Each furnace’s flash codes are different. They’re also called fault codes.
Some codes definitely relate to furnace ignition problems. These error codes include a bad flame sensor or an electric ignition module.
Take the cover off your furnace and look for one or two lights. They might be steady, which usually isn’t an error code. Or it/they could be flashing in a series such one light flashing twice and the second light flashing once.
Near the lights or on the inside of the cover, there should be a key showing you what the flash codes mean. If there’s no key there, like the one below, then perhaps the manual has it.