Forum threads use these three terms almost interchangeably, which causes real confusion when a guide written for a Samsung phone gets followed on a Pixel, or vice versa. They are not the same thing, they are not always interchangeable for the same task, and a phone can genuinely lack one of them entirely depending on the manufacturer.
Fastboot is a bootloader-level protocol most Android OEMs (Google, Motorola, Xiaomi, OnePlus, Sony, ASUS, and others) implement directly. It communicates over USB using the fastboot command-line tool and can flash individual partitions, unlock or lock the bootloader, and read device variables:
fastboot devices
fastboot flash boot boot.img
fastboot flashing unlockThe bootloader unlock state persists across this mode and is what fastboot primarily gatekeeps — a locked bootloader refuses most flash commands outright, returning an explicit error rather than silently failing.
Samsung devices do not use standard fastboot for most flashing tasks. Instead they boot into Download Mode (reached by holding Volume Down + Volume Up while connecting USB on newer models, or Volume Down + Power + Home on older ones), which speaks a completely different protocol compatible only with Samsung's own Odin flashing tool, not the generic fastboot binary.
Some newer Samsung devices do expose limited fastboot support after bootloader unlocking, but it is the exception rather than the rule, and full firmware flashing on Samsung hardware still runs through Odin and Download Mode almost universally.
Emergency Download Mode (EDL, also called 9008 mode after the USB device ID it shows) sits below both fastboot and Download Mode — it is a chipset-level recovery mode built into Qualcomm processors, used to reflash a device so badly bricked that neither fastboot nor the OEM's normal recovery is reachable at all. It requires OEM-signed firmware packages (Qualcomm's own flashing tools, or brand-specific unbrick tools) and is generally a last resort rather than a routine flashing path.
Recovery (stock or custom, like TWRP) is a separate small operating environment used for factory resets, applying OTA update packages, sideloading a signed ZIP, or, on custom recovery, taking a full Nandroid backup. It is not a USB flashing protocol the way fastboot and Download Mode are — recovery mostly operates on files already on the device's storage or pushed via adb sideload, rather than accepting raw partition images streamed over USB the way fastboot flash does.
Flashing a custom kernel or GSI: fastboot (or Odin, on Samsung). Installing a signed OTA ZIP without wiping data: recovery. Recovering a device so broken it will not even show a fastboot or download screen: EDL, if the chipset supports it, using brand-specific unbrick tools rather than generic fastboot commands.
EDL mode is rarely entered through a simple button combination on a working device; it is typically reached programmatically (a specific ADB or fastboot command tells the bootloader to drop into it) or via a hardware test point method on a device that will not boot at all, which is why it functions as the true last-resort layer beneath the other three.
Attempting to flash a fastboot-format image while the device is sitting in Samsung Download Mode simply fails outright, since Odin and fastboot speak entirely incompatible protocols and neither tool recognizes the other's file format at all. This is a safe failure rather than a dangerous one — there is no scenario where a fastboot image gets partially written to a device that is not actually listening for fastboot commands in the first place.