"I don't believe in God, but I believe that there is something bigger than us..."?

I would expect it means that they don't know what it is they think is out there but they think there is something - and they certainly don't want to tie themselves down to any of the current religions and the baggage they carry.

Maybe they are referring to what makes a God. The creator of the creator and so on....

It's that new age god, who is a bit like a karma merchant crossed with mother nature and all the other physics subjects that are difficult to understand, blended in with a good spoonful of buddhism.

They usually mean that they've had a bad experience with a religion and that they don't believe all the doctrine they were exposed to but they believe that there is a power greater than them in the universe.

Means we think organised religion is BS, but that we have a hard time swallowing the scientific theory that states that all life on earth was born out of two giant puddles of primordial GOOP that accidentally and randomly and under certain precise condiftions met to form all life on Earth as we know it in all it's diversity.

Also means we think both religious nutcases and hardcore atheists that preach exactly like them are complete nutcases who are as obtrusive as any Crusades period religious zealot.

It means that they simply don't know what is out there and believe that both stances (for deity/god and against) are on thin ice. Richard has it right. Give him the B.A.

They want to believe in God because that belief makes them feel good and people are not comfortable saying, "I don't know."

It is quite common in the Netherlands. We call it "ietsisme", which translates as: somethingism.

They are usually people who want to believe in something higher without attributing characteristics to it.

They mean that they believe we're not the most advanced beings that exist.

Well, I believe in the power of nature, but I don't believe nature is sentient.