This is the 12095th most frequent Russian word.
известные
"Известные" means "famous" or "well-known."
The word "известные" here is used as an adjective meaning "famous" or "well-known," describing "achievements."
Известные достижения в области науки сделали его имя всемирно признанным.
Famous achievements in the field of science made his name globally recognized.
In this instance, "известные" serves an adjective role, implying songs are "known" or "recognized".
Эти песни известны многим людям.
These songs are known to many people.
Here, "известные" describes "friends," meaning they are widely recognized or famous.