"It's about getting to know who I've become without realizing," she writes. "And I'm sorry it took so long but, you know, life happened."
The title would make sense because her previous two albums -- "19" and "21" -- were about her life during those ages.
In the rest of the post, Adele, now 27, muses about the "life" that's happened thus far, from childhood to the present, writing, "When I was 7, I wanted to be 8. When I was 8, I wanted to be 12. When I turned 12 I just wanted to be 18. Then after that I stopped wanting to be older."
She continues, "I've spent my whole life so far wishing it away. Wishing I was older. Wishing I was somewhere else, wishing I could remember and wishing I could forget, too. Wishing I hadn't ruined so many good things because I was scared or bored ... wishing I didn't know myself so well, because it means I always know what's going to happen in the end."
Addressing the album, she writes that her "last record was a break-up record."
"If I had to label this one I would call it a make-up record. I'm making up with myself. Making up for lost time," she explains. "Making up for everything I ever did and never did. But I haven't got time to hold on to the crumbs of my past like I used to. What's done is done. Turning 25 was a wake-up call for me ... Teetering on the edge of being an old adolescent and a fully fledged adult, I made the decision to go into being who I'm going to be forever without a removal van full of my old junk."
Over the weekend, Adele reportedly premiered a snippet of a song during a 30-second commercial on British TV. The Internet exploded with excitement over lyrics like, "Hello, it's me/I was wondering if, after all these years/you'd like to meet and go over everything/They say that time's supposed to heal ya/But I ain't done much healing."
Since the 2011 release of her last album, "21," Adele has become a mother and settled down with her partner, Simon Konecki, largely avoiding the spotlight.
She emerged in 2013 to collect an Oscar, Grammy and Golden Globe for "Skyfall," her James Bond theme, but hasn't released any new music since. The release date for "25" has yet to be confirmed, but reports have it happening next month.