1. The "A" is the first significant investment by a venture capitalist or very large investor.
In the past, startups raised between $2 and $5 million for their Series A. In recent years, some of the best startups have been receiving well over $10 million from their first venture capital investment. It's been getting cheaper for startups to make more progress with their seed funding, increasing their price when venture capitalists finally invest.
2. The equivalent of an actor landing their first role in a Broadway show – it's an ensemble role but still a big deal...