What is the meaning of IMEI, MEID, ESN, ICCID, SIM, NVRAM

The IMEI - International Mobile Equipment Identity is a unique number to identify GSM, WCDMA, and iDEN mobile phones, as well as some satellite phones. Mostly phone have one IMEI number, but in dual SIM phones are two.

MEID - Mobile Equipment Identifier is a globally unique 56 bits number identifying a physical piece of CDMA mobile station equipment. Equipment identifiers are ‘burned’ into a device, and should be resistant to modification.

ESN - Electronic Serial Number is a unique 32-bits identification number embedded by manufacturers in wireless phones. In addition to being programmed into the phone's microchip, the ESN typically is found on a label under the cellular phone's battery.

ICCID (Integrated Circuit Card Identifier) - A SIM card contains its unique serial number (ICCID). ICCIDs are stored in the SIM cards and are also printed on the SIM card during a personalisation process. The ICCID is defined by the ITU-T recommendation E.118 as the Primary Account Number. A full ICCID is 19 or 20 characters.

SIM card is a microchip in a mobile phone that connects it to a particular phone network. SIM is an abbreviation for 'Subscriber Identity Module'.

Non-volatile random-access memory (NVRAM) is random-access memory that retains its information when power is turned off (non-volatile). This is in contrast to dynamic random-access memory (DRAM) and static random-access memory (SRAM), which both maintain data only for as long as power is applied

NVRAM Firmware of mobilephone is security files use to repair INVALID SIM after damaged the security files when @user Full flashed the ROM via tool to mobile phone.
Nvram firmware is small part of partition of whole ROM of Android device to work well the IMEI, MEID, ESN, ICCID of mobile phone.

IMEI and NVRAM are keeping extremely important data on Android smartphone or tablet mostly Mediatek, Spreadtrum devices. When this data gets corrupt or if you lose the info stored on the IMEI and NVRAM partition, your Android device will not be capable to work on connecting to SIM network at all. you will have to restore your device back to service in order to repair it.