客套話，字面意思是“走錯門”（盪：逛），用於有客人未經邀請或事先未打招呼而上門時。意思說自己門庭不高貴，貴客本不應登門，現在之所以登門，是走錯了的緣故。乜今日咁錯盪啊？（怎麼今天承蒙光臨？）

an expression of courtesy that is used to greet an unexpected guest who drops by to visit to acknowledge them for the trouble they took in coming, similar to phrases like "what brings you here?"