Position - position of the fencer's weapons and body at one point in time. It doesn't matter what was happening before or what will happen after. I.e. Position may be a position in which you have waited, but it also may be a position that you have just passed through.
Action - is about what fencer does in a span of time, typically one tempo. The most common actions are basic cuts and thrusts.
I.33 VS later medieval systems
Later medieval fencing systems are making a clear distinction between a position and an action, and they don't attach any intentions to them. The same cut can be used to strike the opponent or to parry an attack. The cut itself is neutral, it is a choice of a fencer how he will use it. It is similar with positions, that are also not strictly offensive or defensive. On the contrary, I.33 looks at it differently.
Positions of I.33 (wards, custodiae) are never "defensive" in the sense that they are not passively closing any line of attack with the sword. You can wait in them, any offensive or defensive action may be launched from them, but they themselves don't provide any protection beyond a passive protection of the shield. Cuts (sieges, obsessiones) are always offensive, they are never used to parry.
Aside from these, I.33 has schutzen, which are dedicated parries. Schutzen is defined just by its intention, which is strictly defensive - to block the opponent's strike with both sword and shield. And - which is a bit tricky - every schutzen is both a position and an action. If used as a position, it is a position that passively closes one line of attack with a sword. In this way it can defend cuts, but not thrusts (that can go around any static position). If used as an action, it is a cut that goes into the final schutzen position. And as a defensive cut, it can parry a thrust.
The concept of schutzen blurs the line between an action and a position - it is both at the same time.
I.33 seems to be on the edge of older martials and the new ones that we know of. The older martial arts were possibly differentiating actions and positions by its intention (being either offensive or defensive), because this is very natural thing to do. I.33 still keeps this diferentiation in terminology (schutzen = "shelter", which clearly represents the idea of defense), but it already uses it just for its properties, both defensively and offensively.