There may be multiple uses for some of these terms. Fork rake, also called offset, is how far forward of the steering axis the front hub's axle is. There is more information posted on this blog. The term "slack" is often used to describe head tube angles (also described on that blog) that are "slacker" than traditional. There's no real set definition that I'm aware of, but it seems to be used to describe head angles less than about 69 or 70 degrees. The lower the angle, the further away from vertical the steering axis gets. All this stuff definitely influences how a bicycle "feels" or "handles".

(This is one reason I'm a huge proponent in a test ride before a bike purchase...it's sometimes difficult to predict how the bike will feel out on the road just by looking at a few frame geometry numbers.)