In modern music such as as pop, rock and even dance music, there are times when the music builds to a certain high point (may not necessarily be the most intense point, but fairly intense) and then there is a brief "quiet part" in the middle or 3/4 of the track, which is followed by a "intense part" which carries the track the rest of the way until the end.
This "quiet part" could be a moment of silence, or dip in intensity with only a minimal basic beat, or just the vocalist singing quietly without instruments. Sometimes it can even feel like the track has actually ended or will end, until, the "intense part" surprises and excites you with more. In some ways I suppose it also feels like a transition of sorts although you don't realize it until the "intense part".
The "intense part" can be the introduction of a new instrument (eg. an instrumental part after which the vocalist begins to sing), or a new secondary chorus or beat, or perhaps the first point at which all of the instruments can be heard at once. Sometimes it is also the beginning of the track revisited.
Example 1:"Quiet part" starts at 3:03, "Intense part" starts at 3:05 (In the original version the quiet part is much longer and is complete silence, but this appears to have been sped up for the video, you can try pausing the video at 3:04 to get the intended effect).
Example 2:"Quiet part" starts at 6:12, "Intense part" starts at 6:17 (The difference doesn't sound very significant in these 10 seconds, but if listening to the track from several minutes earlier the change here feels like a pretty big difference).
I have done some research and found terminology such as "drop" or "kick line" as well as some other terms from classical music. What is this called exactly?