# Dictionary:Domain

**1**. The set of elements to which a mathematical or logical variable is limited; the set on which a function is defined; the set of values that an independent variable may take. **2**. The class of terms that have a given relation to something is called the ‘‘domain of that relation.’’ Thus, when we speak of a seismic trace in the **time domain**, we mean that time is the independent variable; in the **frequency domain**, frequency is the independent variable; in the *f,k***domain** or *f,k***space**, frequency and wavenumber are the independent variables; etc. **3**. A region of magnetic polarization in a single direction (magnetic moments parallel) that behaves as a unit during change in magnetization. The dimensions of magnetic domains are about 1μm. **4**. The areal extent of a given lithology or environment. **5**. The region occupied by a cluster set in cluster analysis.