# What is the nature of interstitial hydrides?

In my Chemistry book(NCERT Chemistry,Part 2, textbook for class 11, Pg 281). I found the mention of interstitial hydrides:

Unlike saline hydrides these compounds are nonstoichiometric, for example $\ce{LaH_n, TiH_n}$ and $\ce{PdH_n}$, where the chemical composition is variable. Typical formulae are $\ce{LaH_{2.87}, YbH_{2.55} , TiH_{1.8}, ZrH_{1.9}, VH_{1.6}, NbH_{0.7}}$ and $\ce{PdH_{0.7}}$.

The book also said:

Earlier it was thought that in these hydrides hydrogen occupies the interstices in the metal lattice producing distortion without any change in it's type. However recent studies have shown that except for hydrides of $\ce{Ni, Pd, Ce, Ac}$ other hydrides of this class have lattice different from the lattice of the parent metal.

What does this mean? Please explain the nature of these compounds and type of bond present in them.