Series AA Round was a reference to an angel round of startup financing using the YCombinator-developed class of preferred stock called the “Series AA Preferred Shares.” Now, a Series AA Round can be informal label used by some startups and investors to describe an intermediate financing between Series A and Series B, often reflecting an extension, step-up, or additional capital raised after Series A but before a full Series B. In practice, a Series AA Round may be used to reach specific milestones or capitalize on momentum, and Series AA Round terms can resemble either a strong Series A extension or an early growth round depending on market context
