A proper terminology is very important to describe the many shapes of veins and the many different microstructures within veins. The terminology for veins that is currently in use, is mostly derived from Ramsay & Huber (1983) and Passchier & Trouw (1996). I use this terminology, with only minor refinements. Terms for the description of veins can be grouped in three categories. the first two relate to the structure of veins at different length scales, namely:

- macroscopic morphology (e.g. sigmoidal vein)

- microscopic morphology (e.g. fibrous)

The third category, termed "growth morphology" here, relates to the symmetry of the structures (e.g. antitaxial).

Ideally, the geometry and structure of a vein can be fully described by three terms, one from each category (e.g. antitaxial fibrous sigmoidal vein). We will see that not all combinations of terms occur and that some veins have a combination of features (e.g. partly blocky and partly fibrous).