What is the term used to describe the water-holding capacity of soil? 

The term used to describe the water-holding capacity of soil is "field capacity".

Field capacity is defined as the maximum amount of water that soil can hold against gravity after excess water has drained away, typically within two to three days after a significant rainfall event or irrigation. At field capacity, the soil is considered to be fully saturated and plant roots can extract water from it easily.

It's important to note that field capacity can vary depending on the type of soil, its texture, structure, and organic matter content, as well as climatic conditions and land use practices.