Caring for and designing with audio jacks
Audio jacks are... a mess. There are at least 4 different sizes, of which 2 are common, that are called by different names across the Atlantic. There's a variable number of contacts and at least two different schemes for using them. Originally designed for telephone exchanges, they're now used for general consumer audio as well as professional recording equipment. Some are even used for power, for connecting guitar pedals... The "jack connector" may as well be more of an idea than an actual standard.
Nonetheless, in the consumer space, today, there are de facto standard uses for jack connectors. Here, I try to provide an overview of what to expect when tinkering.