According to wikipedia (It might be a rumor, but there is a quote from JC, so...)
Kate is the title of JC Chasez's second solo album scheduled to be released in March or April 2007. He has been working on the album since September 2004.
JC explains meaning of the album name:
“ Kate is an imaginary person that I ended up creating an album around. I wanted to make a record that people could relate to, but I wanted to make it interesting as well. None of the songs are in particular about one person, they’re from a collection of experiences. Each song is about more than one scenario that’s maybe happened to me at one time or another, and since it’s not about one person I kinda had to dream it into this one person to give the record a focus. ”
http://en.wikipedia.org/wiki/Kate_%28album%29