This is the 4641st most frequent Russian word.
длина
Length.
The word 'длина' represents a physical measurement of extent in space in one dimension, applied to the context of a river.
Длина реки составляет тысячу километров.
The length of the river is one thousand kilometers.
Here, 'длина' again denotes a spatial dimension, this time related to a specific object of measurement, a shelf.
Для этой работы нужна точная длина полки.
For this work, we need the exact length of the shelf.
In this example, 'длина' is part of a compound term 'длина волны', referring to the wavelength in a scientific context.