This is the 200th most frequent German word.
vergleich
Comparison.
Here, 'Vergleich' is used as a noun meaning 'comparison' to describe an evaluative comparison between the books.
Ein Vergleich zwischen den beiden Büchern zeigt, dass sie ähnliche Themen haben.
A comparison between the two books shows that they have similar themes.
In this sentence, 'Vergleich' is used in the phrase 'im Vergleich zu', which means 'in comparison to', to compare two days.
Im Vergleich zu gestern ist das Wetter heute viel besser.
In comparison to yesterday, the weather today is much better.
'Vergleich' refers to the act or result of comparing various outcomes in this context.