This is the 738th most frequent Czech word.
důvodů
"Reasons" (genitive plural of "důvod").
In this case, 'důvodů' is again in the genitive plural, used as part of 'z těchto důvodů' meaning 'for these reasons'.
Z těchto důvodů jsme se rozhodli změnit plán.
For these reasons, we decided to change the plan.
Here, 'důvodů' is the word in the genitive plural form, indicating 'of reasons', which is part of the phrase 'několik důvodů' meaning 'several reasons'.
Existuje několik důvodů, proč byste měli navštívit tuto zemi.
There are several reasons why you should visit this country.
Here, 'důvodů' in the genitive plural form is used in the context of the negative structure 'bez důvodů', meaning 'without reasons'.