A city block was an area surrounded by streets on all sides.
In 2268, Bela Okmyx suggested he and James T. Kirk meet at an intersection at the end of the block, near a yellow fireplug. Kirk agreed after Montgomery Scott located the intersection. (TOS: "A Piece of the Action")
In 2293, prior to receiving a distress call from the SS Lakul, the maiden voyage of the USS Enterprise-B was to take the ship beyond Pluto and then return to spacedock; which was a trip that Captain John Harriman described as "a quick run around the block." (Star Trek Generations)