Singer Grimes and SpaceX and Tesla CEO Elon Musk announced Tuesday the birth of their son, who has been named X Æ A-12 Musk.

Musk announced the birth on Twitter, revealing the name in the tweet.

The internet reacted to the news with memes, jokes and humor — something that’s not uncommon with celebrity baby names or with Musk, either. Musk has long been a face of internet meme culture.

But now, Grimes has revealed what the name means.

In a tweet, Grimes explained:

  • X stands for “the unknown variable.”
  • Æ is the elven spelling of AI (love and/or artificial intelligence).
  • A-12 is the precursor to SR-17 (the couple’s favorite aircraft, which doesn’t have any weapons or defenses, focusing on speed).
  • A also stands for “Archangel,” which is Grime’s favorite song.

So, taken those definitions, the name translates as:

“The unknown variable of love and/or artificial intelligence aircraft.”

X Æ A-12 Musk — we still don’t know how to pronounce the name — is the first child for Grimes and Musk together. Musk has two other children — twins Griffin and Xavier, as well as triplets Damian, Saxon and Kai — from his former marriage, according to CNN.

Grimes announced she was pregnant in January.