What is this in the engine bay?

[Qnapper]

Whilst showing friend my camper today was embarrassed that I did not know what this was (picture below) Can someone put me out of my misery please?

 

[DaveD]

Whilst showing friend my camper today was embarrassed that I did not know what this was (picture below) Can someone put me out of my misery please?
View attachment 127282

Power Steering Fluid reservoir.

 

[Qnapper]

Thank you so much. I can sleep now.