Lai See (利是) - or Red Envelopes - are given out for starting to work again on the first working day of the Chinese New Year holidays, usually on the seventh or eighth day of the first month on the lunar calendar (February 14 and 15 in 2016).
The custom is prevalent in Guangdong Province and Hong Kong for signifying smooth work during the upcoming year. The envelopes must be red and gold, as these signify prosperity and good luck. The general rule is that Lai See is given from a senior to a junior: for example, a boss to an employee, parents to children, married couples to single friends. It is not polite to open the envelope in front of the one giving it to you.
(By Jessie Huang, Louis Berney)