text: when did it become customary for people to applaud to show approval or appreciation for a performance?   ok, seester, you asked for it!  the custom of applauding is doubtless as old and as widespread as humanity, and the variety of its forms is limited only by the capacity for devising means of making a noise. among civilized nations, however, it has at various times been subject to certain conventions. thus the romans had a set ritual of applause for public performances, expressing degrees of approval: snapping the finger and thumb, clapping with the flat or hollow palm, waving the flap of the toga, for which last the emperor aurelian substituted a handkerchief (orarium), distributed to all roman citizens (see stole). in the theatre, at the close of the play, the chief actor called out "valete et plaudite!", and the audience, guided by an unofficial choregus, chaunted their applause antiphonally. this was often organized and paid for (böttiger, über das applaudieren im theater bei den alten, leipz., 1822).  when christianity became fashionable the customs of the theatre were transferred to the churches. eusebius (hist. eccl. vii. 30) says that paul of samosata encouraged the congregation to applaud his preaching by waving linen cloths (οθοναις), and in the 4th and 5th centuries applause of the rhetoric of popular preachers had become an established custom.  though, however, applause may provide a healthy stimulus, its abuse has led to attempts at abolishing or restricting it even in theatres. the institution of the claque, people hired by performers to applaud them, has largely discredited the custom, and indiscriminate applause has been felt as an intolerable interruption to serious performances. the reverential spirit which abolished applause in church has tended to spread to the theatre and the concert-room, largely under the influence of the quasi-religious atmosphere of the wagner performances at baireuth. in germany (e.g. the court theatres at berlin) applause during the performance and "calling before the curtain" have been officially forbidden, but even in germany this is felt to be in advance of public opinion.  in most western countries, audience members clap their hands at random to produce a constant noise; however, it tends to synchronize naturally to a weak degree. as a form of mass nonverbal communication, it is a simple indicator of the average relative opinion of the entire group; the louder and longer the noise, the stronger the sign of approval. in other cultures, audiences clap rhythmically in unison, about two claps per second, to indicate approval. clapping in unison might also, however, be understood as disapproval, and an insult to the performer. during musical events, it is common for an audience to clap in the rythm of the song, to cheer the artists present on stage.  famous performers, as well as celebrities in other fields such as politics, may also receive applause when they first appear on stage, before they deliver a speech or their first speaking part. this accolade given in response to his or her past achievements and is not a reflection of the performance the audience is attending.  on some occasions, applause can also occur in the middle of an event. the president of the united states, in his state of the union address, is often interrupted by applause; in fact, tracking the number of such interruptions has become a trend for various television news channels. it is often customary for jazz performers to receive applause in the middle of a tune, after completing an improvisational solo section.  the phrase "slow clap" usually refers to the tentative beginning of applause, especially in american movies from the 1980s (as parodied in not another teen movie). it derived its dramatic usefulness as an indicator of a shift between public scorn and public praise. but at other times the slow clap could be considered insulting or ironic.  (ps thanks dr. dan!)