Electron deficient hydrides are those which have an incomplete octet. They are formed generally by the group 13 elements like B, Al, etc.

Electron rich hydrides are those which contain excess number of electrons on the central atom called lone pairs. These are formed by group 15,16,17 elements like N, O, F, etc.

Now, lewis acids are electron deficient species. They contain an empty orbital which are capable of accepting an electron pair, from Lewis base(electron enriched species) thereby forming Lewis adduct. Eg. FeCl₃, FeBr_3, BF₃, anhydrous AlCl₃, etc. Therefore we can see that hydrides of group 13 can act as Lewis acid as they are electron deficient species.

Likewise, hydrides of group 15 can act as Lewis base as they are electron rich species.