Hi Rimona,

A missed period is basically a month where you don't have a period - some may experience light blood spotting, and some none at all, but you don't have a full menstration.

A few things can cause this: if you're sexually active, it can mean you're pregnant, or if you're severly under/over weight. Some women find that their cycles change and they don't have a period every month. If you've been particularly stressed, that can also affect your cycle. 

If you're worried about a missed period, you should go and see a health care proffesional. You may even be able to go to your local family planning clinic for advice.

Hope that answered your question!