Is to become aware of (something) directly through any of the senses, especially the sight or hearing. This can have a huge impact when it comes to website design and website interaction. For example, when presenting information on a page it must be presented in a clear way to prevent confusion.
A way of dealing with this would be offering multiple ways of receiving the information such as a video or a spoken walk through to make the information more perceivable.
Another key element surrounding perceivability is making sure the design of the platform is easy to navigate quickly and easily. This includes aspects of conventions making sure buttons and drop downs as well as text is clear and well placed.