Spirituality is defined as the quality of being concerned with the spirit or soul as opposed to material or physical things. I think, colloquially, most people define spirituality as religion. I, personally, define spirituality as thinking about the metaphysical questions. There are a lot of questions in the universe that just don't have answers. At least, not answers that can be proven in any direction. Honestly, I'd venture that the answers also don't really matter. I guess "Do these answers even matter?" is probably a metaphysical question in and of itself. Questions like "Why am I here?" or "What makes something right or wrong?". These questions can be answered in a myriad of ways, but at the end of the day. There isn't a "correct" answer.
I feel like religious people will often use "God" or "Religion" to answer these difficult questions for them. To me this seems like the easy way out. I feel like secularists, often, have to deal with these questions in much greater depth. When you can't just chalk up your life's purpose to a deity, it's a lot more difficult. Generally, you have spend a lot of time reading, researching, contemplating, and discussing these topics. And a contemplative person may see their answers to these questions evolve as they experience more of the world and learn new things.
So my definition of Spirituality is vague and difficult to pin down. It's like a lantern floating down a raging river. At any one point you may be able to see the light, but sometimes it dips out of sight of is tossed behind a rock. But the lantern is almost never in the same spot twice.