So, as it seems, there is some "misunderstanding" of the term "mids", imo ... however this is something really important to know, if you intend to know how your sound is created!
What we are talking about here, is the dividing of the frequencies you hear (from 20hz up to 20khz roughly) into three areas:
BASS
MIDS
HIGHS
there are no real, normed, borders, it's rather as some part of orientation term.
The Mids range from something like 300Hz to 7kHz, and carry the acustical information of the sound, so to speak (What instrument it is, f.exp).
As the mids are so important, some people tend to divide between lower mids (those with lower frequencies) and higher mids (those with the higher frequencies).
Concerning the guitar, the higher mids are the part, where you get aggressive / sharp / fizzy (together with highs) / piercing / saturated elements to the sound, they help you a lot to get your sound into the front position.
the lower mids are the define how fat or dry / big / muddy (to some degree, together with the BASS) / dark your sound gets, for example.
Hope this helps at least a little bit : )
PS: in your sound, everything plays a role - from pick to strings to pickups, bridge& hardware (does make a very noticable difference), guitar construction and wood, cable (maybe not much), amplifier, cab (very strong influence!) to the room itself. so what you need depends on the rest of gear, imo
