The first number is the number of bedrooms, 1-2-3-4 etc., L is living area, D is dining area, and K is kitchen. Thus, 1LDK means 1 bedroom with a living area, dining area, and kitchen. Not all properties have a LDK though, some may say 1K or 1DK, especially in big cities like Tokyo and Osaka. 1K being 1 bedroom with a kitchen and 1DK being one bedroom with a kitchen and dining area. There are also a few properties that are 1R, this means that there is only one large room that will serve as your bedroom and kitchen (like a studio apartment). The kitchens in these apartments are usually quite small, so if you love cooking, this type of apartment will limit you. And finally, there are some apartments that may have “S” in them, like 1SLDK. This “S” stands for service room (some may refer to it as a storage room), though it could be used as a free room as they can vary widely in size. These types of rooms could be a small walk-in closet, to the size of a small bedroom. In the latter case, a 1SLDK could also be viewed as a 2LDK.