populär
popular
Known, liked, and appreciated by many people.
Dieser Popsong war in den 90er Jahren extrem populär.
This pop song was extremely popular in the 1990s.

popular
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popular
Known, liked, and appreciated by many people.
Dieser Popsong war in den 90er Jahren extrem populär.
This pop song was extremely popular in the 1990s.

To express within which group someone or something is popular, 'populär' (popular) is often used with the preposition 'bei' followed by the dative.
Diese Art von Musik ist besonders bei jungen Leuten populär.
This type of music is especially popular with young people.
The adjective 'populär' (popular) belongs to the word family around the noun 'die Popularität' (popularity). If something is popular, it enjoys great popularity.
Die Popularität des Schauspielers ist seit seinem letzten Film stark gestiegen.
The actor's popularity has risen sharply since his last film.
In the meaning 'for the general public,' 'populär' (popular) is very often part of the word 'populärwissenschaftlich' (popular-science). It describes the understandable presentation of science for non-experts.
Ich lese gerne populärwissenschaftliche Bücher über Physik.
I enjoy reading popular-science books about physics.
known
'bekannt' and 'populär' both describe that many people know something or someone. However, 'populär' usually also has a positive meaning: many people like or appreciate the person or thing. 'bekannt' only means that something is known; it does not have to be liked. So you can be 'bekannt' without being 'populär'. The confusion arises because famous people are often also popular, but that is not always the same thing.

Die neue Serie ist bei Jugendlichen besonders populär.
The new series is especially popular among teenagers.
Der Politiker ist sehr bekannt, aber nicht alle mögen ihn.
The politician is very well-known, but not everyone likes him.