In one sentence
In a securitization, the party holding the loans for the benefit of bondholders and administering the trust per the governing documents.
The longer version
The trustee holds legal title to the securitized loans and administers distributions to bondholders under the pooling and servicing agreement. It is a fiduciary role defined by the deal documents.
Trustee requirements shape certain loan-level mechanics, especially around assumptions, modifications, and defeasance.
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