A special purpose vehicle is a legal entity created for one narrow job - in tokenized assets, holding a pool of securities or other reference assets so that tokens can be issued against it. The SPV isolates those assets from the issuer's other business: if the issuer fails, the SPV's holdings are meant to remain the token holders' claim.
When a tokenized-stock program says its tokens are backed by securities held in an SPV at a custodian, that structure - not the issuer's promise - is what the claim rests on.
Issuer structures differ by program and are disclosed per family; U.CASH asset pages link the issuer's own documentation rather than paraphrasing it, and diligence sections state what each program's setup does and does not guarantee.
Every term behind the rails, the assets, and the settlement.