Passive Usage of 言う

A plain form sentence + と言われている is often used to express something like "It is said that..." or "It is said to be..." This is common in written texts to explain a concept or describe something.

風邪を引いた時はビタミンＣをたくさん取るといいと言われている。
It is said that when you catch a cold, you should take a lot of Vitamin C.

女の子は男の子より頭がいいと言われている。
It is said that girls are smarter than boys.

世界で一番長い川はナイル川だと言われているが、アマゾン川だと言う人もいる。
It is said that the Nile River is the longest river in the world, but there are also people who say that it's the Amazon River.

チョコレートは野菜よりいいと言われている。
It is said that chocolate is better than vegetables.