: Indicates an open-plan area that combines the living, dining, and kitchen spaces into one cohesive "great room."

Urban Dictionary and meme archives show no entry for 1ldkjk . However, fragmenting it:

In essence, a 1LDK is a one-bedroom apartment where the kitchen, dining, and living areas are combined into one relatively spacious room, separate from the sleeping quarters. It is the gold standard for young professionals, "power couples," and retirees who want more breathing room than a tiny studio (1K) but don't need a multi-room family home. Decoding the "JK"