Sitzprobe literally means a 'seated rehearsal' and it's a term used in opera and musical theatre to describe the time when the singers first get together with the orchestra, before a production is presented publicly. The aim is for the two groups, the singers and the musicians, to put the music together. The equivalent Italian term is prova all'italiana, which sounds to me as though it should mean to test everything in Italian, but obviously doesn't.
Tonight the cast and orchestra of Grimhilda! will hold their sitzprobe. The use of the word has had most of the cast asking, What the heck is a sitzprobe? because I don't think it's a term usually used in amateur musical theatre circles. Perhaps people doing amateur opera use it; I'm not sure.
I'm familiar with it because in the days when I worked with opera singers, the term came up constantly, and the event itself was always interesting. The singers would get all theatrical and start to show off, and the musicians would turn on their slightly superior looks and pretend that actors/singers and musicians should barely be allowed in the same room. However, after the initial impact of having to sit down together and get the thing moving, they'd all become friendly and it would go swimmingly.
Well, 'swimmingly' might be a bit optimistic: it would go fairly well, because the first meeting of the singers with the orchestra is always quite stressful for the singers. They've been working for weeks with nothing but a piano, and suddenly all those sounds they've been used to have been transformed into sounds they aren't used to, and it's quite off-putting. Nothing sounds right.
Which is why we hold sitzprobes (I'm sure the German plural is something different, like sitzproben, or whatever, but I don't actually know). Tonight is going to be interesting, to say the least!