Internal transcribed spacer (ITS) is a commonly used term in molecular biology to describe the non-coding regions between the ribosomal RNA genes in eukaryotes. While ITS is the most common term used, there are a few synonyms that refer to the same thing. These include intergenic spacer (IGS), intergenic transcribed spacer (ITS), and non-transcribed spacer (NTS). These terms have the same meaning and can be used interchangeably. The ITS region is an important tool in studying the evolutionary relationships among organisms, as it evolves quickly and is highly variable, making it a useful genetic marker for species identification and taxonomy.