Can someone explain to me the difference between passive wisdom and perception please?
Passive Wisdom could apply to any situation where the DM wants to use your Wisdom ability as a benchmark (DC) or for secret rolls based on your Wisdom.
Passive Perception applies to situations where the DM thinks that specifically your ability to notice things is what is important, versus, say your ability to judge truth or apply medicine. If you're not proficiency in Perception, a Perception check becomes a Wisdom check instead. That's why it'll generally be listed as a Wisdom (Perception) check.
As Perception is by default a Wisdom-based skill, an untrained character's Passive Perception = Passive Wisdom, both functionally and numerically.
If the character is proficient in Perception, then Passive Perception should be 2 to 6 points higher than Passive Wisdom, based on level.
I must have missed something here, Where in the book is the mention of passive wisdom? I'm not saying it's not there, just that I must have missed it 
I assume this comes from the character sheet that says "Passive Wisdom (Perception)," which technically is just a way of saying Perception's "full name," like Strength (Athletics) or Intelligence (Investigation).
Skills are often listed in this way, first by ability, then by skill, to reinforce the idea that any skill check defaults to a simple ability check for the nonproficient.