Conversion Trigger
On a convertible note this is the monetary amount that would trigger a conversion of the note to equity, associated with a financing where equity is purchased by investors. It's often written in the note purchase agreement as a "Qualified Financing" where the conversion trigger is listed as "the aggregate of $X...".
For example
If a convertible note has a conversion trigger of $5,000,000 it will remain through maturity, or until the company sells more than $5,000,000 of equity.