For which scenario is a tile backer board typically used?

A tile backer board is specifically designed for use in environments that are exposed to moisture, making it an essential material in wet areas such as showers. This material is impervious to water, thus providing a stable and durable substrate for tile installation, which is crucial in preventing water damage, mold growth, and other issues associated with moisture infiltration.

While backer boards can sometimes be used in other situations such as ceilings, they are not the primary recommended choice for those areas; other materials might be more suited. Moreover, it is not appropriate for use under hardwood floors, as those installations typically require a different kind of underlayment that can accommodate wood expansion and contraction. Thus, the specific suitability of tile backer board in wet areas is what makes it the correct answer in this context.