Metric Modulation is just a fancy term for changing time signatures, a technique that should be in the tool box of any musician. In this video Jor shows how to start in one signature (4/4) which transitions into a (3/4). The goal, of course, is to make this sound as smooth as possible.
There are multiple ways to do this, but a very effective method is to use a melody that works in both signatures, as shown in the video. All in all a cool simple trick which you can use in any style of production.
1:15 Example 1
3:10 Example 2
5:40 Creating an Interlude