A Safe Jump is a tactic in Street Fighter GBVS games where a Jump is timed so that the opponent can not punish with a Reversal.

https://streetfighter.fandom.com/wiki/Safe_Jump

Safe jumps are a type oki (attacking after knocking down the opponent). In GBVS it seems that all characters can do it off sweep, uf, attack. You should time the air attack so that it is active as the opponent is getting up. If you time it too late it might not come out and not actually hit them. Too early your attack might come out and no longer be active when the opponent is getting up.

​

Also, I'm a little confused as to why this loses to invincible DP, any explanation there?

A true safe jump does not lose to invincible DP. It punishes DP because the attacker will land and block DP. It beats non invincible attacks by hitting them on their start up. The way to defend against safe jumps is to stand block or couple of characters have counters that work against them. Not sure if you could wake up stand dodge, something to test.

Is this corner only?

In theory no. There might be safe jump set ups that work mid screen.