A security chip used in Apple's products.  Isolated from the CPU, the Secure Enclave Processor (SEP) stores private keys for encrypting data in storage as well as for authentication to websites.  The Secure Enclave is built into mobile devices starting with the A7 processor and Macs using the M series chips (see 
Apple A series and 
Apple M series).
Secure Enclave is the Apple equivalent to the TPM in PCs and KNOX in Samsung devices (see 
TPM and 
Samsung KNOX).