The Vietnamese word "khi trước" means "formerly" or "before." It refers to a time in the past, indicating that something happened at an earlier point in time compared to now.
"Khi trước, tôi sống ở thành phố khác."
(Formerly, I lived in another city.)
"Khi trước, thời tiết ở đây rất lạnh."
(Before, the weather here was very cold.)
You can combine "khi trước" with other time expressions to provide more context, such as "năm ngoái" (last year) or "khi tôi còn nhỏ" (when I was small).
"Trước đây" is another phrase that can be used similarly to "khi trước." It also means "before" or "in the past."
While "khi trước" primarily means "formerly," it can also indicate a general time reference without specifying how far in the past something was, depending on the context.