This is the 461st most frequent Japanese word.
一番
"Number one; the best; most; first."
In this sentence, 一番 is used as a superlative, indicating 'the tallest' in the context of comparing heights within the class.
私はクラスの中で一番背が高いです。
I am the tallest in the class.
Here, 一番 is used to express liking something 'the most' out of a comparison or selection.
この映画が一番好きです。
I like this movie the most.
In this example, 一番 serves as 'first,' referring to the sequence order of trains arriving.