This is the 457th most frequent Chinese word.
小时
Hour.
Here, '小时' is used to indicate a duration of time—one hour.
我每天早上五点起床，跑一个小时。
I wake up at five every morning and run for an hour.
'小时' is used to specify the amount of time spent on an activity.
他花了两个小时完成了这个报告。
He spent two hours completing this report.
In this sentence, '小时' denotes a recurring interval of time—every hour.