Practically speaking, I think it is whatever combination of piano + _____ that a pianist can get paid to play with.
I apologize for immediately focusing on paid employment, and sidestepping any reference to artistic merit, pianistic training and study. Believe me, I am aware of the complex depths of knowledge that pianists need to spelunk in their university-led studies of Collaborative Piano. I have come to realize, however, that those hard-earned skills are often best used in a university/academic setting. [the phrases often and best used were chosen deliberately] Opera houses are the next useful setting.
Which is fine. Especially if one's passion is in the area of instrumental collaboration or opera and art song interpretation, etc, and their wish is to specialize in those areas.
But outside of the university environment, I found that knowledge of opera, art song and Brahms sonatas, while neat, was less in demand. Alternate piano skills were requested. For example:
- sightreading 4+-part choral scores (often mentioned, but not always enforced as something to actively study in the university setting)
- sightreading musical theatre/musical theatre score interpretation
- being an audition pianist
- knowledge of jazz repertoire and voicings
- knowledge of musical styles - latin, funk, etc
- knowledge of pop music
and so on.
I've also noticed that outside academia, timelines are different as well. Getting music in advance is a luxury, and sightreading has become the norm. Requests to accompany auditions and concerts are often last minute (for which you can charge accordingly). Limited rehearsal time can lead to you waltzing out onstage with no idea what your partner is going to do. Scary? Yes. But sometimes, that's the gig. My point: employable in multiple venues = flexible. Mentally prep yourself for situations that are not ideal. Study improvisation. Observe and eventually play for vocal and instrumental auditions. Add regular score sight-reading to the [already busy] practice schedule, etc. Get used to performing on the fly. In other words - diversify your skill set, both at the keyboard and mentally.
Classical piano training is an asset in so many ways - but one's training and education needn't stop there. Especially if you enjoy variety in your work. My goal for this blog is to call attention to the spectrum of educational and employment opportunities available for those who wish to play well with others. And not only in the University setting.
While I'm at it - here's a website from along the same lines, that I like: musicianwages.com. It has great information on ways to find playing gigs, including being a cruise ship musician. You don't have to be a jazz player - there are positions available playing as a part of a classical ensemble (with at least one string player). The site is geared towards all working musicans, of all backgrounds, so there's something for everyone. Check it out.