Horizon Debt

Horizon Debt. Means up to $15,000,000 in principal and interest due thereon owed by the Company under the Venture Loan and Security Agreement dated as of May 24, 2005, as amended on September 1, 2006 and from time to time, by and between the Company and Horizon Technology Funding Company, LLC and the Notes (as defined in such Venture Loan and Security Agreement).