This means that by learning a few shapes, you will have the ability to play a wide number of chords, provided you know where the root is in each shape for each chord.
What is an inversion? The first chords you probably learned all had the root note in the bass, on the sixth or fifth string. But if you find a different root on an 'upper' string, you can construct the same chord with the same strings as your original fingering. The new chord will be an inversion -- it will have some other note (the third, seventh, or fifth, e.g.) on the bottom.
What makes a chord voicing "drop 3" or "drop 2" has to do with how the notes would be written out on a staff. It's probably more useful to know what string the root is on and what note is in the bass (the bottom note). You will hear musicians refer to a chord as "F with A in the bass" or "Fmaj7 over A" or "Fmaj/A". These are all the same chord. What it means for the jazz guitarist is an Fmaj7 fingering with the 3rd as the lowest note.
It is good to know all the inversion of any chord you know. Practice moving the chord up the guitar neck using different strings as the roots. Make sure you are conscious of AT LEAST the root note every time you lay a voicing down.
The attached PDF shows moving basic chords up the neck in all their inversions. Some of them are virtually unplayable, but you should still be able to 'see' them on the fretboard. Try mustering a fingering that does not use the root, as that will often be fine for comping with a bass player, who states the root anyway.
Notice that the same shapes appear again and again, only the roots and intervals are different. For example, a Major6 chord will have the same shape as a Minor7 chord. If you use the 6 of the Major6 to be the root, it will be a Minor7 chord.
This is known as "chord plurality." Another set of 'homonyms' is Minor6, Minor7b5, Dominant9(no root) and Augmented Dominant7b9. The intervals of all these chords are the same shapes. Once you know one shape, you get three more chords as a bonus!