Squire is a title, accorded to a number of sorts of individual. A squire could be a prominent landowner or English country gentleman, a local judge, or a nobleman in training, who attends a knight. Such a young nobleman could be the son and heir of a higher-ranked nobleman, but as a squire, he ranks below the knight he serves.
In 2267, the USS Enterprise encountered an alien who identified himself as 'General Trelane (retired) - now just Squire Trelane'. Considering the setting this alien had manufactured, it is likely that he was using the term in the sense of a principal landowner. He had manufactured a largish fortified manor (or smallish castle, depending on one's definition) as part of his guise. (TOS: "The Squire of Gothos")