Describe intersymbol interference.

What will be an ideal response?

When an RF signal is transmitted, it does not take a direct path straight to the receiver. Instead, multiple copies of the signal are transmitted, and these various copies may bounce off objects in the area before reaching the receiver at slightly different times having traveled along different paths, a phenomenon known as multipath.  Although the difference between the signals, called delay spread, is so small as to be measured in nanoseconds, it can still affect reception because these copies are "added" to the primary signal. Known as intersymbol interference (ISI), this adding of signals to the primary signal can result in downfade, corruption, or nulling.