I am asking this question in light of a situation I witnessed recently:
When the senior rabbi of our shul--a very righteous man who was keeping his wife's yahrzeit that night--walked past the audience to come to the stage, a few people seated on the end of the front row nearest him stood halfway up, or possibly stood up and bowed.
What were they doing and what are the details of this custom? Who, what, when, and where do we do it?