This is the 5050th most frequent Russian word.
метра
"Метра" in English means "meters" (plural form of the unit of length).
In this sentence, 'метра' is the genitive singular form of 'метр' because it follows the quantifier 'кило-', dictating the genitive case due to Slavic numeral agreement rules.
Он живёт в километре от метро.
He lives a kilometer away from the subway.
Here, 'метра' is in the genitive plural form; this case is used after numbers 2, 3, and 4 for objects being measured, describing the height of the ceilings.
В этом здании потолки высотой три метра.
The ceilings in this building are three meters high.
In this example, the word 'метра' is also in the genitive plural case following the number 'два', conforming to Slavic plural numeral case usage.