What does Ex dividend mean?

When a company's ordinary shares goes Ex-Dividend, it means that from the date that the share went Ex, the shares no longer trade with the benefit of a dividend.

So, if the ex-dividend date is 20th June, then if you buy the shares on or after that date you will not qualify for the latest dividend payment. If you bought on the 19th June, then you would qualify for the dividend.

In the UK, Shares always go Ex-Dividend on a Wednesday.