This is the 266th most frequent Icelandic word.
undanfarin
"Undanfarin" means "recent" or "preceding."
Here, 'undanfarin' is used as an adjective modifying the noun 'ár' (years) to indicate a period of time immediately preceding the present.
Undanfarin ár hefur fólkið í bænum lagt meiri áherslu á umhverfisvernd.
In recent years, the people in the town have placed greater emphasis on environmental protection.
In this sentence, 'undanfarin' describes 'kvöld' (evenings), suggesting a few specific evenings prior to the current one.
Henni hefur liðið betur undanfarin kvöld eftir að hún breytti mataræði sínu.
She has felt better in recent evenings after changing her diet.
The word 'undanfarna' (an inflected form of 'undanfarin') modifies 'viku' (week), indicating the week leading up to the present time.