A serial number is a unique number assigned by the manufacturer (like Samsung) to help identify an individual device, like a phone, tablet, TV, and so on. For example, your phone's serial number will be different from every other phone Samsung has made. Serial number makes it easier for the makers to organize and keep track of their products.
On the other hand, an IMEI or MEID is only used for phones or other communication devices. Depending on the carrier, your device will have either an IMEI or MEID. These two numbers are different from a serial number. They are used at an international or global level, not just by manufacturers. Both types of numbers can help network providers track down a device that has been stolen or lost.
A model number is a specific number that applies to a range of products (i.e., Galaxy Note20, Galaxy Z Fold2, etc.). The number will vary depending on the year the product was released, its color, the carrier, and some other factors. Every model that falls into that category (same color, etc.) will have the same model number.