I was to a violin concert and at the end of the concert, when the audience applauded, I saw some of the violinists beating their pointer fingers or palms softly with the bow. What is this? Is this a kind of collegial applause?
Yes that is one way members of the string section applaud. Another way that all members of the orchestra can do that is to shuffle their feet. It’s a sound that is easily heard by other orchestra members but hard for the audience to see or hear. I’ve read of it being done even during performances after an especially good solo or cadenza.