Meaning of single and double entry visa

Usually the validity of a Single Entry or Double Entry "L" visa is 90 days or 180 days from the date of issue. This means the holder of the visa shall enter China no later than 90 days or 180 days from the date of issue, otherwise the visa will be expired and is null and void. Normally the duration of stay of a "L" visa is 30 days, which means the holder of the visa may stay in China for up to 30 days from the date of entry.