What are "Full range speaker"

The standard understanding is that a full range speaker is one capable of producing the audio spectrum from 20Hz to 20kHz.

Your Spendors are considered by many to be full range, but they do miss the bottom octive. True 'full range' have an 'open' bottom end, or no restrictions to how low they will play. There are very few true 'full range' speakers. Even though the term 'monitor' can apply to large multi-driver speakers, it is generally used to describe small box speakers, 'full range' usually refers to floorstanding and other large speakers. Its just a general way to describe the type of speaker. You would list your Spendor S8 speakers as 'full range' here at Audigon.

Usually referred to single driver speaker and not 2,3 or 4 way speakers

Aside from what's mentioned above, Aside from the book shelf and small monitor speakers, almost all the non-single driver speakers today are full range speakers