A trading statement is an announcement that has limited, but sometimes very important, disclosure. The essential part of a trading statement is some sort of update on a company's revenues: for example sales numbers and sales trends. In addition it is not uncommon for companies to reveal some other performance indicators, but, even then, it would not be usual to reveal any profit numbers: unless a surprise requires that the market be given a profit warning.
Trading statements allow analysts and investors to refine, and sometimes drastically revise, forecasts and valuations. Apart from total sales, other information, such as changes in the sales mix may change estimates of margins, and of growth prospects.
Trading statements are often issued as the last announcement to the market before the start of a close period. This allows the market to be reasonably up to date until the results announced at the end of the close period.