pci dss – What is two full-length key components, PCI DSS 3.5.3 requirement

PCI DSS 3.5.3 Standard

3.5.3 Store secret and private keys used to encrypt / decrypt cardholder data in one or more of the following forms at any time:
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At least two full-length key components or key actions, according to a method accepted by the industry

Could you leave me what the full-length key components, what is the relationship with secret and private key storage? AS QSA, how do you check if the verified part fulfills the condition? Thank you very much ~