An art show with one artist is a solo show. One featuring many artists is called a group show. What in the generally-accepted industry term for an art show that only has two artists? A dual show? A duo show?
A "group exposition" or "collective exhibition" could be used to describe a two person art show ... BUT (after searching the internuts a bit) it seems that "Duo Exhibition" is the most common term for a two artist show. Group Exposition or Collective Exhibition applies to shows which have three artists or more.
In the exhibition guidelines for the MacDonald Island Community Art Gallery Exhibition they list three categories of exhibitions which depends on the number of artists showing: Solo, Duo and Collective
SEÇİL BÜYÜKKAN gallery discussing the Seçil Büyükkan and Deniz Aktaş "Hande Şarman" show refers to the event as a "Duo Exhbibition".
The CV for visual artist Yooree Yang gives a listing of Solo Exhibition & "Duo Exhibitions" the artist has participated in the past
I think this really can depend on the artists purpose or goal. I found a Google book called Fine Art Publicity: The Complete Guide for Galleries and Artists that talks about this. What little we can see for free that is pertinent talks about creating press release for these refers to them as Multiple Artist and Theme Exhibitions.
An article discussing a (at the time) future exhibition featuring two artists as just that: An exhibition. The search that led me had the subject:
Francis Bacon & Henry Moore: Terror and Beauty
One could argue that it was a themed art exhibit. In this case the two artists were from the same period, drawing on a similar war torn past into their works, but never collaborated together during their lives.
As we can see in the other answers there are multiple terms in use to describe this. I think the goal of the artists and hosting gallery or venue will drive what terms they would use to describe their exhibition/exhibit. I don't think there is one answer for this.
I've often seen two-person exhibition used to describe this kind of show. A simple web search on the term brings up a number of examples.