Secure Element

From The Apple Wiki

The Secure Element (or SE) is the NFC/ApplePay chip. This chip is codenamed Stockholm. Firmware packages for the chip are codenamed Icefall and use the .sefw file extension. Internally, the firmware packages seem to be divided into sections marked with the magics SLALOM_PACKAGE, CRS_PACKAGE, and FTA_PACKAGE.

Apple's description of ApplePay and the Secure element: https://support.apple.com/en-us/HT203027