I would recommend doing some YouTube tutorials on charging your Tesla to get a broader answer to your question. Search something like "Mobile Charging adapters Tesla".
In short "14-50" is an outlet type designated by NEMA. The pin configuration is type 14 and it can handle 50 amps. This outlet supplies 2-3x the power of a standard household outlet (think dryer, electric stove, welder outlets).
The adapter referred to is for the Mobile Charge kit so it can connect to that type of outlet. The Mobile Kit now comes standard with only a NEMA 5-20 outlet (the standard residential outlet). A few years ago the kit include both the 5-20 and 14-50 adapters, but now you have to purchase the 14-50 separately if you want it.
Its important to know that there are many outlet types out there. You get purchase them one at a time or there is an entire bundle kit from Tesla here that has some of the most common types:
Maximize your charging options with the NEMA Adapter Bundle. Simply attach the appropriate adapter to your Mobile Connector, plug into the corresponding outlet and begin charging. With all seven Gen 2 NEMA Adapters in one convenient storage bag, you can charge at any available outlet, at home or...
shop.tesla.com
Many people only get the 14-50 as it is somewhat common (I believe it is the standard RV connector so many RV parks have this outlet). I personally have a NEMA 6-50 (what my garage is wired for) adapter and a 14-50 adapter.
The main use case for these is either getting your setup at home figured out, or planning to charge at personal destinations like friends, family, RV parks, etc.
Hope this helps!