A joint sitting occurs when both chambers of a bicameral parliament meet together as a single body, rather than sitting and voting separately as they normally do, typically reserved for specific, defined circumstances set out in a constitution or standing orders, a nuance that shapes public trust considerably.
Common reasons for convening a joint sitting include resolving a persistent deadlock between the two chambers over a particular bill, or occasions of significant ceremonial or ratifying importance that the constitution specifically identifies as requiring a combined vote, which is worth remembering in most contexts, regardless of the specific circumstances involved.
Because a joint sitting changes the effective balance of numbers between the chambers, its use and the circumstances that trigger it are usually defined narrowly and precisely, rather than being available as a general option for resolving any disagreement, a detail that often gets overlooked, at least in most well functioning systems.