The interior or inner part.
The inside of the building has been extensively restored.
The left-hand side of a road if one drives on the left, or right-hand side if one drives on the right.
On a motorway, you should never pass another vehicle on the inside.
The side of a curved road, racetrack etc. that has the shorter arc length; the side of a racetrack nearer the interior of the course or some other point of reference.
The car in front drifted wide on the bend, so I darted up the inside to take the lead.
(in the plural) The interior organs of the body, especially the guts.
Eating that stuff will damage your insides.
A passenger within a coach or carriage, as distinguished from one upon the outside.
Guts, intestines, innards