This is the statute that sets out what claims in bankruptcy are secured claims. This is the text of 11 U.S.C §506(a).
§ 506. Determination of secured status
(a) An allowed claim of a creditor secured by a lien on property in which the estate has an interest, or that is subject to setoff under section 553 of this title, is a secured claim to the extent of the value of such creditor’s interest in the estate’s interest in such property, or to the extent of the amount subject to setoff, as the case may be, and is an unsecured claim to the extent that the value of such creditor’s interest or the amount so subject to set off is less than the amount of such allowed claim. Such value shall be determined in light of the purpose of the valuation and of the proposed disposition or use of such property, and in conjunction with any hearing on such disposition or use or on a plan affecting such creditor’s interest.