Often we hear people complain that an explanation is too theoretical, whereas the real obstacle to understanding is that it is not precise enough. I would proceed like this:

A chord symbol is a short denotation for a collection of (typically three or four) note names, not specifying an octave for any of them. To be played as an actual chord, each of these notes must sound in one or more octaves. (Obviously, if six strings are to sound three note names, some of the latter must occur more than once.) On the guitar, the choice of these octaves (commonly called "voicing") is mainly restricted by technical considerations (- fingering). However, we do have some options. In many situations, one voicing/fingering is best suited musically (for reasons to be explained in lesson 214), whereas another one is easier. The choice of lowest note is particularly important musically (see lesson 215), therefore often specified with the chord symbol, separated by a slash.