写字楼 is a Chinese term for 'office building', distinct from 办公室 (an individual office room). It refers to a commercial building with multiple floors of office spaces, often found in business districts. In mainland China, 写字楼 is the standard word for a dedicated office building, while 办公楼 is also common but can include government or institutional buildings. You'll hear it in real estate contexts: 写字楼出租 ('office building for rent').