Closed Period
Before a listed company announces its financial results it usually adheres to a so-called close or closed period. The close(d) period differs per company, spanning a few weeks period (e.g. three weeks or as of the first of the month following the preceding quarter) for quarterly results, and longer for annual results.
No inside(r) trading in close(d) period
The close(d) period is intended to prevent trading in company's shares by insiders before the publication of its financial results.
Insiders may be privy to information that is not yet in the public domain, which could be considered price-sensitive and may have an impact on the share price. Consequently, they are not allowed to trade in the company’s shares (assuming they have shares in the company) prior to publication of the results. Besides the legal consequences for anyone who is involved in insider trading, it most likely will also have a negative effect on the reputation of the company. To help prevent this, a company has the obligation to compile an insiders' list of people that have access to price-sensitive information.
Those people who are on this list are not allowed to trade in the company’s shares during close(d) periods.