Bounce rates are extremely important when it comes to analysing an Adwords campaign. If a visitor clicks on your ad and visits your website and then leaves on the same page without clicking through or interacting with the website then they are counted as a bounce. The bounce rate is recorded as a percentage of the total visits, so for example, if the bounce rate is 50% then half of your visitors are leaving at this stage.
A High bounce rate (above 30-40%) can indicate a problem with your site or a problem with your keywords / adverts within Google Adwords. You need to have a look at the ads and keywords that have the highest bounce rate. Check that they are relevant to what you are selling and that they are going to the correct page within your site. It is often not advisable to send every ad through to the home page if there is a more relevant page.