sndos

it means sound, the snd part is an abbreviation for sound.
the Scottish/Irish/Northern-English slang word sound, on its own would mean good/cool and you could describe a person as being sound.

however, sndos is typically used by Scottish teenagers on snapchat to say alright thats good.

an example of a typical conversation using sndos.
"come tae ma gaff around 8ish" said kellyanne
"sndos x" replied her pal