1K", "2DK", "3LDK"... and so on are examples of how to describe the floor plans of condominiums and single-family homes.
The numbers represent the number of rooms.
L = living room, D = dining room, K = kitchen.
Example: On the left is a typical floor plan for a 1LDK and on the right is a typical floor plan for a 2DK.
LDK has a large living room and a separate kitchen, while DK has a small living room and no separate kitchen.
Difference between 1K and 1DK
In the case of 1K and 1R, there is no dining room and only a little space for a kitchen.
On the other hand, 1DK has a separate room and a larger kitchen area.