What is solitude? Is it good? Why?

I was answering this question (which was about whether people have a difficult time finding solitude to be in, or difficulty in being alone with their thoughts) and I started to realize that a) I didn’t exactly know what people meant by “solitude,” b) people seemed to think solitude was good, but I couldn’t tell if that was a consensus or not, and c) no one was talking about why they valued solitude.

I want to find out what solitude means to you—i.e., what are the physical/mental qualifications for solitude. In particular—is interacting with people on fluther count as solitude? What about letter writing where you receive one letter per month. What if you received ten letters a day? Is solitude a mental or a physical thing? If it is mental, what are the boundaries of solitude for you? You should consider other forms of communication ranging from face-to-face to video, voice, instant messaging, email, etc.

Second—do you value solitude? Do you hate it? Somewhere in the middle?

Third—why do you value or hate solitude? What does it do for you? How does it help or hurt you?