Click chemistry refers to using a tag molecule that will react with biomolecules irreversibly. They do not have to be 1,3 dipolar cycloadditions. There are also retro diels adler [4+2] or azides reacting with alkenes [3+2]. 

At the same time, not all 1,3 dipolar cycloadditions meet the requirements for click. The simplest I can think of is click reactions must be water compatible, which is not the case for many cycloadditions.

Basically, not all click reactions are 1,3 and not all 1,3 reactions are click. What Click chemistry demands are reactions that occur easily, irreversibly, in water and usually non-toxic. Any water sensitive 1,3 cycloaddition (for example some reactions that use grignard reagents as catalysts or dihalocarbenes) is not a click reaction.

Dear Shrikant Pharande:

As Tomâs Allende, already mentioned, the criteria for a reaction to be considered a 'click' process is to be both thermodynamically and kinetically favored, clean and, if possible, in water.

Even the archetypal azide-alkyne 1,3-cycloaddition is only a click procedure when a) copper is used as catalyst (kinetics is tuned so reaction ocurrs very fast) or b) a strained, cyclic alkyne is employed (reactant is destabilized). In these cases, the reaction proceeds smoothly. Otherwise, the same reaction carried out thermally (Huisgen cycloaddition) is indeed quite endothermic and yields a mixture of isomers.

Summarizing, not all 1,3-dipolar cycloadditions qualify as click reactions.

Best

Mauricio

Dear Shrikant, click reactions can be further classified as : a)cycloadditions ie, Huisgen reaction b)nucleophilic opening of highly strained rings c)non-aldol type carbonyl chemistry and d)addition reactions of alkenes and alkynes i.e.thiol-ene reaction or Michael additions. As general click reactions ocurred in one pot and joint two different motifs. Kind regards

thank you guys