Short for "later dude". Used to signify departure, disapproval, or denial. Appropriate for use in all situations: when someone is leaving a conversation online; when exiting a formal dinner with business associates; to suggest disagreement with another person, etc. Can also be pronounced as a full word: "uld".
"You want me to buy YOU lunch? Uhh...LD."
"$4000 a month? Hahahahah....LD."
"Take care folks. It was good to see you, as always. I look forward to doing business with you. LD."
"I agree with sections A 1.5 through C 2.7, but everything after section C 2.7 can get the old LD. No, really. LD."