High Functioning Autism (HFA) refers to the level of functioning an individual with autism has at their disposal for everyday tasks. HFA defines not only whether an individual (such as myself) has autism, but where on the autistic spectrum they are.
In contrast to this is 'Low Function Autism' which refers to an individual who has less functionality in carrying out every day tasks.
Neither of these define an autistic individual's mental capacity toward emotional, cognitive, spacial, mathematical, abilities, only the individual's capacity toward carrying out "normal" activities such as personal care.
HFA is interchangable with Asperger's syndrome/disorder (after the discoverer, Hans Asperger; this is set to change in the DSM/V whereby the two may be merged into a single term, or diagnosing one will cease and only one of the two definitions will continue, unless Asperger's is differentiated from HFA (something which has yet to take place).
The 'high functioning autistic' (HFA) person wakes up in the morning and proceeds to get ready for the day. They're able to communicate and solve problems on they're own. The don't need to be supervised and have their own opinions, thoughts, or ideas. They may drive to work, talk at length with a work colleague, or completely refrain from discussion at work while working very hard at their job with a sense of purpose unlike many others.