Traffic is a measure of the number of users that visit a website. Traffic is an important metric to measure for an SEO strategy, but beware the numbers.
Many SEOs wrongly believe that there job is done when traffic coming from search increases. However, if this traffic is not the intended audience for the website, they are unlikely to convert to the websites goals and are pretty useless.
The real job of the SEO is to bring more qualified users likely to convert to the websites goals. For example, if you manage to coax a thousand male football fans to a childrens' ballet website where the goal is to signup to a ballet course, you will have no conversions. In terms of traffic you're strategy is working, but in terms of effectiveness, your strategy is a complete failure.
Traffic is often referred to as a vanity metric - it's easy to make yourself feel good about getting more users to a website, but are they really worth the effort.
In your analytics programme you should split your audience into different groups - location, gender, whether they are new or returning users, etc. – to find out if your strategy is really attracting your target audience.