"Pace" is supposed to be the speed or effort at which you plan on doing the ride for which you are training. You can measure this in average speed, speed on the flat, average heart rate (HR), rating of perceived exertion (RPE), or power, depending on the measurement technology available to you. RPE or HR are the best, as speed will vary with the terrain, and the terrain on your target ride will probably be different than the terrain on your training rides.
"Brisk" means go harder than pace. Make your legs tired. OTOH, don't go all out. Don't go any harder than you can recover from in a day. The idea is that your body will adapt to the faster pace and in time your Brisk speed will become your Pace speed. You get much faster if you push yourself from time to time. And you might discover than you are dogging it on the Pace rides!