[Samsung Galaxy S20 / S20+ / S20 Ultra Questions & ] epsilon0:
I'm also new to the CSC concept, and have been looking into its function. I would recommend checking out these links for a good overview.

(I'm a new user and cannot post external links, you'll have to use a search engine to find these. If a MOD wants to change these to links, feel free!)

1 - Droid Views dot com- "Difference Between CSC and HOME_CSC (Samsung Firmware)"

2 - Droid Views dot com - "Change CSC on Samsung Devices – Samsung CSC Codes"

3 - Samsung dot com - Tech Talk - "What’s CSC on Samsung?"

4 - Android dot stackexchange dot com - "How to find my device's CSC (Country Specific Code)"

5 - https://xdaforums.com/showpost.php?p=72198850&postcount=21

6 - https://xdaforums.com/showpost.php?p=72321531&postcount=28

7 - technastic dot com - "CSC or HOME CSC? Which File You Should Flash in Odin"

8 - https://xdaforums.com/showthread.php?t=1988202

9 - https://xdaforums.com/showthread.php?t=2033894

10 - https://xdaforums.com/showthread.php?t=1356325

11 - Android dot stackexchange dot com - "What do the numbers and letters in the Samsung Firmware mean?"

12 - https://xdaforums.com/galaxy-s3/general/csc-codes-t2090739

What follows are my findings and my attempt to 'put it all together'.

Samsung Firmware Naming Convention

See [10] and [11]

What is a CSC?

Samsung CSC refers to the Country Specific (Product) Code. This identifies the region and carrier for which the device is configured [1,3].

This includes [7]:

Carrier branding: A CSC may be country or carrier-specific. Samsung releases the same model of a smartphone to Tab with different CSCs. For instance, if you use an unlocked or unbranded Samsung Galaxy phone in the UK, its CSC would be BTU. However, if your device is locked to a network operator, it could be VOD (Vodafone), TMU (T-Mobile), ORA (Orange), XEU (EE & Three), etc.

System Languages: These include the availability of the popular languages used in a geographical area. For example, if you own a Samsung phone in Mexico and flash the firmware meant for India with INS as CSC, you won’t be able to set Spanish, Nahuatl, or Mixtec as your phone’s system language and keyboard.

Localizations: Samsung ships its devices with geo-specific or bloat apps relevant to a country or region. Localization also determines the calendar settings and local festivals.

APN Settings: Access Point Name settings include all configurations to make a mobile device work with the network carriers of a region or country. Without these configurations, you may not be able to enjoy seamless GSM, GPRS, 3G or 4G mobile networks.

Samsung FUS: CSC also contains key info to help Samsung’s Firmware Update Server to connect to the correct update channel and roll out the proper software update to your Galaxy device via OTA.

Deep dive:

Historically, Samsung had one CSC folder on the device [8], located at /system/csc. This folder contained different XML files used to configure the device.

/system/csc
features.xml
language.xml
others.xml
customer.xml

The supported configuration options for these files have been extensively documented by other users [9].

Presently, there are two flavors of CSC files CSC and HOME_CSC. Flashing CSC performs a factory reset of the device; wiping all third-party apps, data and settings [7]. HOME_CSC is used to reinstall the firmware or updating the system, retaining apps, data, and settings.

Examining the current contents of a HOME_CSC file shows the structure has changed.

HOME_CSC_OMC_OXM_G985FOXM3ATG9_CL18862671_QB33041563_REV01_user_low_ship_MULTI_CERT/
meta-data
cache.img.lz4
optics.img.lz4
prism.img.lz4

The three image files correspond to directories found on the device root (using adb).

/cache/
backup
backup_stage
lost+found
lsb
magisk
magisk.log
magisk.log.bak
recovery

/optics/
configs

/prism/
HWRDB
app
etc
lost+found
media
priv-app
sipdb

Buried within the optics folder, we find XML files similar to the original design.

/optics/configs/carriers/single/TPA/conf
cscfeature.xml
cscfeature_network.xml
customer.xml
omc.info

How do I find and interpret my CSC?

You check your CSC by going to Settings > About Phone > Software Information > Service Provider SW Version. According to [1] you should see the following, depending on your phone's SIM capacity.

Where, according to [5]

Some phone info applications call these the original (CCC), firmware (AAA), and active (BBB) CSCs. For example, my SM-G985F shows

SAOMC_SM-G980F_OXM_TPA_QQ_0006
...
TPA/TPA,TPA/TPA

Which tells me that the phone was manufactured for Panama, has the Panama firmware and the recommended SIM CSCs are both for Panama. I know this because the list of CSC country codes is well documented [12].

NOTE: I came across multiple sources online that say the SIM CSC will change depending on the SIM card you have inserted. For example, [1] states

But this may not be true. I am in the USA using a local provider and was never prompted as described.

What does each CSC do?

So we have the three different CSCs, each of which could be responsible for configuring different parts of the phone.

Firmware

SIM

Original (factory)

I would think that the original CSC is only there to identify the original factory firmware, and is not configuring anything on the phone. The firmware CSC should tell me the current firmware loaded and the SIM CSC does ???

I will continue to look into this over the next few days. If anyone can contribute more information it would be very helpful.