Flora and fauna have subdivisions that group members by certain traits or uses. Fauna can be described as megafauna or microfauna, meaning very large or very small animals respectively. The subdivisions of flora are not usually based on inherent traits, but instead refer to the ways humans use them. For example, agricultural flora is the plants used for crops, while weed flora is those plants that are undesired in a particular region. Microorganisms, such as bacteria and fungi, are often informally included in subdivisions such as gut flora or skin fauna. The terms fauna and flora have often been used interchangeably when referring to these microorganisms since they do not fall into the domains of plants or animals. Instead, many biologists prefer the term microbiota when discussing microorganisms.