年間

1. Origins, structure, and basic meaning

• Structure: 年間 is read as ねんかん and marks either an annual frame or a duration of a stated number of years.
• Basic usage: 年間利用者数 is an annual count, while 三年間 means a period lasting three years.

2. Common pitfalls and similar expressions

• Annual frame
  • Before a measure, 年間 indicates that the figure is counted or considered over one year.
• After a number
  • In 三年間働く, the expression measures how long the work continued rather than listing three separate calendar years.