This is the 7066th most frequent Spanish word.
este
"Este" in Spanish means "this" (demonstrative), "east" (direction), or "this one" (pronoun), depending on context.
Here, 'este' is used as a demonstrative adjective describing the noun 'libro' (book), meaning 'this' in reference to something near the speaker.
Este libro es muy interesante.
This book is very interesting.
In this sentence, 'este' is again a demonstrative adjective, modifying 'problema' (problem), used to point out a specific issue being discussed or addressed.
¿Qué piensas de este problema?
What do you think about this problem?
Here, 'este' is part of the phrase 'este momento' (this moment), indicating a specific point in time current to the speaker.