Let 
, 
and so on.
A stream is a sequence of channels S, such that:
n is the number of channels in the stream S. In other words, the channels must define values for the same period of time.
Intuitively, a stream represents monitoring a set of channels, rather than just a single one. To continue the above examples, what if we not only wished to sample forefinger bend, but also wanted to sample the bending of all the other fingers; and even wanted to sample information such as the orientation of the hand? A stream allows us to collect all these various measurements and treat them, in some ways, as part of the same ``event''. There is also an idea that the above mathematical representation does not make clear: for a given element of the (shared) domain of the channels, the value of the channel somehow represent measurements at the same ``time''.