van is a preposition in the Dutch and Afrikaans languages, meaning "of" or "from" depending on the context (similar to and in the Romance languages).
van is a very common prefix in Dutch language surnames, where it is known as a tussenvoegsel. In those cases it nearly always refers to a certain, often quite distant, ancestor's place of origin; examples of this in English can be found in the names Greta Van Susteren "from Susteren" and Rembrandt van Rijn "from the Rhine".
In surnames, it can appear by itself or in combination with an article (compare French de la, de l'). The most common cases of this are van de, van der and van den, where the articles are all current or archaic forms of the article de "the". Less common are van het and van 't, which use the similar but neutral article het. Common is also the contraction ver- of van der, which can be written as a single word with the rest of the surname; an example can be found in Johannes Vermeer (van der meer "of the lake").
The German "von" is a cognate of Dutch "van", though unlike the German "von", the Dutch "van" is more often part of a common surname than an indication of nobility or royalty. It can both imply nobility (Willem van Oranje "William of [the] Orange [family]") or signify any ancestral relation to a particular place (Jan van Ghent "John [who hails] from Ghent").