SPoD - Stun Palm of Doom
GBoD - Guard Break of Doom/Death.
They are short terms that were converted so that people don't have to say the full name of the moves or the notations all the time. The Doom or Death part is that in the Virtua Fighter game, they had a lower health base and it did a lot of damage for someone attacking/blocking.
Think it had something to do in the name meaning, translation, and the way the string was shown, but I honestly couldn't really tell you. It does feel better writing it in English or shorten it to three letters (DLC).
Akira has two versions to it, which is Iron Lean Combo (the simplified P+K one, Hontei Goko Hazankou) and Dragon Lance Combo (Hantei Goko Tensetsukou) which ends in the 466P+K from 3H+K. Had to copy and paste that because it feels weird just writing it, so I can see why they had to come up with terms for those.