Standard Connector for Audio Line Out
Afaik, there is no 'default'.

There are many more types:


5 pin DIN (very old, obsoleted by RCA); mono or stereo per connector





RCA (2 different plugs for stereo), mostly obsoleted by 3.5 or 6.3mm jack plugs; mono per connector





Jack plugs (3.5mm used in most consumer devices), 6.3mm for more high-end devices (in general), mono or stereo per connector





XLR plugs (mostly 2 plugs for stereo), used by 'professional' sound equipment; mostly mono per connector. Also these plugs have the advantage to 'lock' themselves.




All of the above can be used for input or output audio.