Section 363 of the bankruptcy code controls sale of property of the bankruptcy estate by a debtor. 

Ordinary Course of Business
Sales of property of the estate may generally be done without a court order if in the ordinary course of business. Ordinary course of business generally refers to past business practices of the debtor. A secured creditor with an interest in property that is not otherwise cash collateral must take affirmative action to prevent the sale of property in the ordinary course of business. 

Outside of the Ordinary Course of Business
Sale of property that is not in the ordinary course of business may take place only "after notice and a hearing."

Sales Free and Clear of Liens
Property encumbered by liens may be sold subject to liens or "free and clear of any interest in such property," such as lien holders. A sale free and clear relieves the purchaser of obligations on the liens and the lien is transferred to the proceeds of the sale. Section 363(f) of the Bankruptcy Codes sets forth the conditions for a sale free and clear.

It should be noted that the Bankruptcy Code does not define "interest in property" of which the property is being sold free and clear, but it clearly includes liens and security interests on the property. The precise limits of the meaning of "interest" is dealt with in the case law.