The bolt pattern of a wheel is the physical arrangement of the bolts or studs that hold it onto an axle. The bolt pattern can be 5 lug, 6 lug, 7 lug, etc. depending on how many bolt holes there are to secure the wheel to the vehicle.
Each bolt circle has its own bolt pattern designation determined by multiplying the number of bolt holes in each circle by the bolt hole diameter. This bolt pattern designation is then divided by the bolt hole diameter and multiplied by 1000. This will give you the bolt pattern size (diameter) in millimeters.
The bolt holes on many wheels are not round; they can be oblong, hex shaped, or self-ejecting. Also, the bolt holes may or may not fit a bolt with a standard head. If one bolt pattern does not fit onto your vehicle, try another bolt pattern that is listed as being compatible.
Bolt pattern size of wheel may or may not match bolt pattern size of factory wheel on vehicle. Bolt holes have a tolerance that is plus or minus 4 mm of the stated bolt hole diameter.
If the bolt pattern does not match the bolt pattern of the vehicle, the wheel may have to be machined down to a bolt circle diameter that will fit your vehicle. Wheel center cap may or may not be able to cover bolt holes on wheels with non-round bolt holes.
The lug nuts that secure the wheel onto the axle need to match the bolt pattern size of the wheel. If your bolt pattern size of wheel is 5 lug, you will need five lug nuts to secure it onto your vehicle.
If a vehicle's bolt hole bolt circle diameter is too big for the bolt pattern on the wheel that you are trying to bolt onto the vehicle, then bolt holes may have to be machined in order for bolts with standard heads to fit the bolt circle diameter of vehicle bolt holes. Bolt pattern size designation may not be the same bolt hole diameter designation.
More information you can find at https://wheelssize.com/bolt-pattern/