There are two definitions of "sample" in TouchDesigner.
In CHOPs, it is a single number, where a sequence of samples makes up a channel.
In the audio world, "sample" often means what in TouchDesigner would be called a channel, or two channels where the audio is in stereo. In TouchDesigner, we refer to it as a CHOP holding two channels with a certain time duration, measured in (Touch-style) samples, seconds or frames.
In the context of TOPs, we sometimes talk of "sampling an image".