Senior debt is the most senior layer in a borrower's capital structure. It's the first claim on cashflow for interest payments and the first claim on assets if the borrower defaults and security is enforced.
For property-secured lending, senior debt typically means a registered first mortgage. The lender holds the first-ranking charge on title and has priority over second mortgages, caveats, unregistered interests and unsecured creditors.
Senior debt prices lower than subordinated debt because the risk position is materially safer, for an asset to lose value below the senior debt amount, every layer below it (equity, mezz, second mortgages) has to be wiped out first. The trade-off is yield: senior debt yields are lower because the risk is lower.
Archer Wealth's entire loan book is senior secured first-mortgage debt, by design, because the wholesale trust structure that funds the book sets that as an eligibility criterion. This is the same structural protection that distinguishes a senior secured private credit fund from a high-yield credit fund holding mezz or unsecured paper.