The symbol \(x\) represents a function that represents a signal. It can either be continuous, in which case it will look like \(x(\htmlId{tooltip-time}{t})\), or discrete, in which case it will look like \(x[\htmlId{tooltip-wholeNumber}{n}]\), where n is a whole number \(\htmlId{tooltip-wholeNumber}{n} \in \htmlId{tooltip-setOfWholeNumbers}{\mathbb{W}}\), representing the sample number by the analog to digital converter.