Q:

What's the difference between orientation and position?

In INS (Inertial navigation system) sensors, is there a distinction between the following?

Orientation (heading, pitch and roll) 
Position (latitude, longitude and altitude)

Is the orientation relative to a specific axis while the position is absolute? If yes, what is the axis?

A:

Yes there is a distinction, pitch, roll and heading are angles [unit = radian] and latitude, longitude and altitude are linear distances [unit = meter].  Together, these six parameters define the six Degrees of Freedom that define the momentary state of a rigid object with reference to the earth.
All six are defined relative to earth axes. For the linear dimensions this is clear, we just need to define a suitable zero point. For the angles:

Pitch is the nose up/down angle relative to the gravity field of the earth.
Roll is the wingtip up/down angle relative to the gravity field of the earth.
Heading is the angle relative to a suitable earth reference, usually magnetic north or geographical north. 

Conversion of aircraft axes into earth axes is a non-trivial matter and the cause of much confusion, for instance in questions comparing lift to weight: lift is always coupled to aircraft axes, weight to earth axes. The axes sets are defined as follows:
Aircraft axes

Origin: Centre of Gravity of aircraft
X-axis: in the symmetry plane of the aircraft, + = forward to the aircraft nose
Y-axis: in the span wise direction of the aircraft, + = to the right wingtip
Z-axis: perpendicular to the XOY-plane, + = down into the floor.

Earth axes

Origin: Centre of Gravity at the start of the response
X-axis: In the horizontal plane (relative to gravity), + = pointing north.
Y-axis: Perpendicular to XOZ-plane, + = pointing east.
Z-axis: Pointing to the centre of the earth = +

Edit
Yes navigation lat/lon is given in [degrees] - the INS sensor ultimately converts displacement into proper navigational definitions of course. But for measuring 3-D aircraft inertial effects the SI system is used, and displacement is internally treated as a linear motion, units [metres].

A:

Position is where you are; orientation is which way you're pointing (including any roll).

