Autism is a life-long neurological condition. It is known as a "hidden disability" because you cannot always distinguish whether someone has autism.
As of 2012, the consensus from the National Autistic Society indicated that the statistics for Autism, in the UK alone, was 1 in every 100 people said to have an autism diagnoses - figures are now expected to be approximately every 1 in 88 (UK) will have a type of autism diagnoses. http://www.autism.org.uk/about-autism/myth-facts-and-statistics/some-facts-and-statistics.aspx
Typically, you will hear the term 'Autism Spectrum'. The term spectrum simply means that there are a number of different forms of autism. The type of autism all depends on how the person functions.
There is no 'cure' for autism however it can be managed by medications to counteract the effects and certain people may find that it will help them to function better, depending on the advice given from health professionals. However, medication does not make autism 'go away', it is a life-long condition.
You may notice that someone with autism may have a lack of eye-contact when talking face-to-face with another person.
Those with autism can find communication difficult as it can be a stressful experience for them, and this is because often they do not filter information as well, and so understanding can be more difficult.
Using simple phrases can be helpful - and people on the spectrum will often take things literally so you need to be clear and understanding.