What do you mean by activity and selectivity of catalysts?

Explanation

Activity of catalyst `:` The ability of a catalyst to increase the rate of a reaction is called activity. For example,
`H_(2)+1//2O_(2)rarr `No reaction.
`H_(2)+1//2O_(2)+[Pt] rarr H_(2)O+[Pt]`
`(` explosion and very fast reaction takes place `)`
Selectivity of catalyst `:` It is the ability of a catalyst to direct a reaction to yield a particular product. For example, both dehydrogenation and dehydration of ethanol are possible. But in the presence of a suitable catalyst only one reaction is made to occur.
`CH_(3)CH_(2)OHunderset(573K)overset(Cu)rarrCH_(3)CHO+H_(2)(` dehydrogenation `)`
`CH_(3)CH_(2)OHoverset(Al_(2)O_(3))rarrCH_(2)=CH_(2)+H_(2)O(` dehydration `)`