1. next, coming, approaching [adjective] [‘aan-staan-du’]

"Aanstaande" literally translates to "onstanding". It is used to indicate that the adjective’s subject is about to happen/become (true) in the near future.

Sometimes, you may find "aanstaande" placed behind its subject. This is only the case when it is used in the context of a time adjunct. In that case, "aanstaande" is often abbreviated to "a.s.", see the Examples.

Examples:
– "Wanneer is de vergadering?" – "Aanstaande donderdag om tien uur."
("When is the meeting?" – "Next/This Thursday at ten o’clock.")

– "Wanneer is de vergadering?" – "Donderdag aanstaande om tien uur."
("When is the meeting?" – "Next/This Thursday at ten o’clock.")

– "Wanneer is de vergadering?" – "A.s. donderdag om tien uur."
("When is the meeting?" – "Next/This Thursday at ten o’clock.")

– "Wanneer is de vergadering?" – "Donderdag a.s. om tien uur."
("When is the meeting?" – "Next/This Thursday at ten o’clock.")

– "Er wordt gezegd dat aanstaande moeders veel augurken eten."
("It is said that expectant mothers eat a lot of pickles.")

– "Het tijdperk van de mens is ten einde, het tijdperk van de ork is aanstaande…"
("The age of man is at an end, the age of the ork is near/imminent…")

Related words:
– "Komende": coming.
– "Volgende": next.

2. fiancé(e), future husband/wife [noun] [de aanstaande, de aanstaanden] [‘aan-staan-du’] 

In this context, "aanstaande" is essentially short for "aanstaande vrouw/man": wife/husband to be. There’s also the synonym "verloofde", but this word has quite a formal connotation.

Examples:
– "Mag ik u mijn aanstaande voorstellen?"
("May I introduce my fiancé(e) to you?")

– "Wie is de vrouw die zo zit te mekkeren?" – "Dat is Franks aanstaande…"
("Who is that wining woman?" – "That’s Frank’s future wife.")

Related words:
– "Verloofde": fiancé(e).
– "Zich verloven": to get engaged.
– "Verloving": engagement.
– "Trouwen": to marry, to get married.