domain (idea)

Among other things

• The set that a function takes a value from. A function maps one set (its domain) to another (its range or codomain depending on how fussy you are). The domain is defined by the fact that the function assigns a value to every member of it (and to nothing outside it), and assigns exactly one value to every such member. It is symbolized dom, as in dom f.
• An exon, that is an active subregion of a gene, that is not necessarily transcribed, where the gene can have several alternative realizations depending on environmental conditions.
• A region of a magnetized material that is locally all the same polarity. (I think.) If this is not just a fiction of my poor memory, magnetic domains break down at the Curie temperature. (I think.)