Click chemistry is a concept introduced by K. Barry Sharpless in 2001 and describes chemistry tailored to generate substances fast and reliable by joining small repeating units together in the same way as nature does. Its poster boy is the azide alkyne cycloaddition.
In a recent essay in Angewandte Chemie (DOI) Barner-Kowollik/Du Prez/Espeel/Hawker/Junkers/Schlaad/van Camp warn that the original definition formulated by Sharpless has become corrupted. They identify at least 20 reaction types now labeled as a click reaction that do not meet the original specifications. Emphasizing the impact of click chemistry on polymer science they reiterate the main points: a reaction product should be isolated by nonchromatographic methods, such as crystallization or distillation, the reaction should give very high yields, quickly proceed to completion, with reagents readily available and reaction products stable. A reaction may be efficient but not a click reaction when the criterion of equimolarity is not met. Most reactions listed as click fail the wide in scope requirement. The term click should be handled with more caution otherwise the authors state it may become over time a synonym for - successful - and thus largely irrelevant and meaningless. So noted!