I was toying with the idea of Max (the non-computery person here) actually not knowing what a RAID array was, but then I figured that most of my readers might also not know, so I think this works better. A RAID array is when you have multiple hard drives that duplicate your data, so if one goes bad, you don't lose stuff. Pretty self-explanatory.
But yeah, this is how I define "depth" - something that can be appreciated on multiple levels, for different reasons. It's why, although her work deals with economics and philosophy that are normally considered highbrow, I don't consider Ayn Rand's writing to be particularly deep. She isn't really talking about more than one thing at a time.
It's worth noting that, by this definition, a deep novel doesn't have to be particularly long, nor does a deep relationship have to be particularly long-term. Depth also has no bearing on intensity - a parent's love for their baby is one of the strongest loves in the world, but you'd have a hard time convincing me their relationship is deep.
(Thursday evening, INT: Overdrive Computers, back room)
MH: Okay, wait. I'm curious. Ellen - how exactly do you define "deep" versus "shallow" relationships? Just by genuineness of affection, how deeply the emotion is felt?
EB: That's like asking me to define what love is. But sure, I'd say it's about genuineness of affection.
LH: No, no, that can't be right. Puppy love - like, love from an actual puppy - is as genuine as it gets, but I wouldn't call that a particularly "deep" relationship.
GU: I think it's like a deep versus a shallow novel. Deep ones have multiple layers, there's more going on than just the plot on the surface, you can talk and think about them for hours.
MH: That makes sense. A deep relationship is like multiple relationships stacking on top of each other - sexual compatibility, common interests, et cetera. That way, if one thing fails - he goes broke, she gets ugly - the relationship doesn't immediately break down. There's other things holding them together.
LH: So a deep relationship is a love RAID, is what you're saying.
MH: No, a "love raid" is more like the surprise party that Gina got to peek in on two weeks ago. What I'm describing is more like some sort of redundant array of inexpensive disks.