Jaar means year. The plural is jaren (years).
The singular form jaar is often used in Dutch where English would use the plural. Jaar is more commonly used for a specific number of years and jaren for an unspecified numbers of years, but there are no fixed rules and people do not always follow grammar rules anyway. The easiest to remember is that jaren is always plural and jaar can be either singular or plural.
Some common uses:
- 5 jaar oud – 5 years old
- In het jaar – in the year
- Vorig jaar – last year
- Twee jaar geleden – Two years ago
- Enige jaren geleden – Some years ago
- Sorteer op jaar – Sort by year.