Leona did a good job of getting the basic meaning across. Technically, cis is a Latin prefix meaning something like "on the same side of", whereas trans means "on the opposite side of."
For similar reasons, too. Both groups tend to be relatively invisible because they can fall back on straight/cisgender privilege. For many it's quite possible to remain entirely closeted and live a fulfilling life. That double-edged sword makes things much simpler until recognition would be useful. Then it gets very difficult because it looks like you've been doing fine all along, and no one can imagine why you'd want to complicate your life. It can go the other way, too. My aunt is bisexual but dated women primarily until she met and married a wonderful man. I'm sure there are some in the family who think of her as an ex-lesbian instead of bi.As Rog pointed out the Bs sort of fall betwen the cracks as they may also be in the CD community.
Only because you picked a silly name. We already do use gay to refer to lesbians, queer to refer to everyone in our community, and LGBT really is a collective term we use with enormous regularity. It's not so silly, after all. As individuals it may make sense for us to quibble with terminology and try to describe how we feel, but as a group it's politically valuable to align interests. You could also argue that another fairly common term for all of us is "gender variant." Attraction to the opposite sex is just one of many presumed norms.I ask you to consider working publicly to eliminate the entire population calling themselves G or L or B or T and just lump them altogether and call them "the different people"? Silly isn't it?