simply put, you aren't likely to move through things that are harder than you, such as brick walls but will move through softer things than you, such as air.
...THAN YOU is the relative bit.
'real' is one rotational energy experiencing another rotational energy. this is often called 'sub-atomic structure'.
you are real relative to like, perceptible energies.
or not. that's up to you- belief is also relative, after all!!