"The dots" refer to the Fed's periodically updated economic projections.
"Periodically," in this case, means 4 times a year out of the 8 annual Fed meetings.
"Economic projections" is a misleading term, not because the Fed isn't actually publishing such a thing, but rather, because no one really cares what the Fed thinks GDP and job growth will do. Markets are only interested in the part where each Fed member says where they think the Fed Funds Rate will be by the end of the year as well as at the end of the next few years.
This rate hike outlook is conveyed via a dot plot in the Fed's Economic Projection materials. And that's why you're just as likely to hear "dots" in reference to the whole darn thing. In any event, when I say "dots," I'll be referring specifically to "The Fed's rate hike outlook released concurrently with other economic projections and the official policy announcement at 2pm today."
With that housekeeping out of the way, today is all about the dots. We already know they're going to hike--true foregone conclusion. They could also change a few words in the announcement, but unless those changes give some indication that the Fed rate hike cycle will soon be winding down, they'd be hard-pressed to hold a candle to the dots. All of the above happens at 2pm, but there's also the Powell press conference at 2:30pm. Markets are still getting a feel for his style, so we definitely can't rule out market movement potential there.
And if all this weren't enough, there's still a strong possibility that the biggest market movement of the week could follow tomorrow's European Central Bank announcement, or at least that we wouldn't see today's full effect until we hear from the ECB. Either way, the next 24 hours are high stakes.