What does R3 mean?

[Litbelb]

What does R3 mean/stand for?

[_az]

This post explains the naming:

@jsha

We’re using O=Let’s Encrypt, CN= E1 , E2 , R3 , and R4 to identify intermediates, where E/R indicates the key type, and we chose non-overlapping numbers across key types to make the names even easier to visually distinguish.

[griffin]

R = RSA

E = Elliptic Curve (EC)