The natural reverberation of concert halls adds a lush and pleasant ambience to music. However, those halls are not available during recording sessions in studios, thus creating the need for artificial reverberation without being dependent on a specific location.
Early attempts to produce reverberation featured echo chambers, which were specifically designed pleasantly sounding rooms often with tiled or hard stone walls to reflect sound waves. An audio signal would be played back on a speaker at one side of the room and then be captured via microphones at the other side, including the room's ambience, to simulate large concert halls. In some instances producers used even as little as an office bathroom for a wet signal to dial in for drums, vocals and synths. Many great echo chambers are still in use today and are even available as a plugin.
During the late 50s, EMT introduced the EMT 140 plate reverb, which contributed to many popular hit records by bands such as Pink Floyd or The Beatles. An electromechanical transducer attached to a huge sheet metal plate created vibrations that were picked up by contact microphones. Those could be added to the dry signal and even be adjusted in duration by a remote-controlled dampening pad. The most famous units are still in use at Abbey Road Studios and also available as a plugin today. A similar principle was used in spring reverbs, utilizing the vibration of long metal springs rather than plates, allowing for a much more compact size of the units. Spring reverbs were especially popular in organs and guitar amplifiers, even available to semi-professionals due to their modest cost.
Even in the 80s, lots of reverb can be a bad thing and quickly muddy your mix. It is, therefore, fundamental to apply as much as needed, and as little as possible. A listen to your entire mix when tweaking your reverb. Never just on a single track or instrument, as reverb is perceived quite differently when soloed.
It's good advice to fade down the entire reverb until you barely notice it, then turn it down a bit more for good measure. Now listen to the mix and give your ears some time to adjust. Even if they trick you into thinking your mix is too dry, it might still be way enough reverb. There is an easy trick to check: Disable the reverb completely, and you should notice a huge difference.