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.”

Of or pertaining to the inner surface, limit or boundary.

“The inside surface of the cup is unpainted.”

Nearer to the interior or centre of something.

“All the window seats were occupied, so she took an inside seat.”

Originating from, arranged by, or being someone inside an organisation.

“The reporter had received inside information about the forthcoming takeover.”

Within or towards the interior of something; within the scope or limits of something (a place), especially a building.

“It started raining, so I went inside.”

Indoors.

“It was snowing, so the children stayed inside.”

Intimately, secretly; without expressing what one is feeling or thinking.

“Are you laughing at us inside?”

Within the interior of something, closest to the center or to a specific point of reference.

“He placed the letter inside the envelope.”

Within a period of time.

“The job was finished inside two weeks.”