HID bulb in size 9007 come in three options: bi-xenon (one bulb switching from a low to high beam due to a magnet in the bulb itself), Lo/Hi Halogen (Xenon bulb for Low beam and Halogen bulb for High beam on the same bulb base) and Single beam (only one beam can be upgraded in with this option). The choice depends on your vehicle. If you have two headlights you can choose between first two variants. If there are four headlights in your car, it means you need single beam bulbs. 9007 bulbs are used to replace your vehicle's OEM bulbs with the same corresponding size.
To make sure that this is the correct bulb size for your car lights, you can look it up on the bulb itself or in your car owner’s manual.