It's a fuse - a resettable PTC.
It's resistive and when it heats up because of the current flowing through it, it gets more resistive which limits the current. When it cools down, it allows current to flow again.
The advantage is that this protects your circuit from temporary faults without having to replace the fuse because of them. A temporary fault can be caused by the user or a specific situation like a motor that is jammed.
I accidentally tested one yesterday - it got quite hot but normal operation was restored in about 30 seconds.
The symbol is a non-linear intrinsic variable resistor by the IEC standard
In this case the part is a "polyswitch" PTC thrermistor self-resetting fuse
So the intrinsic variablility is that it's a thermistor and the non-linear feature is the sudden increase in resistance that theses parts have.
I can tell it's a polyswitch by the refdes
F1 indicating a fuse and the
500mA indicating the trip current for the part.