Glossary
Defuse
In one line: Defusing the spike: 7 seconds in total, with a checkpoint halfway.
What it means
On defense you also win the round by defusing the planted spike. It takes 7 seconds, with a checkpoint at 3.5 seconds: if you stop after the halfway point, the next defuse resumes from there. The defuse has to finish before the spike detonates.
Some variants have names: the half defuse (reaching halfway and stopping to fight), the fake defuse (tapping the defuse to bait out a hiding enemy) and the ninja defuse (defusing quietly while the attackers do not notice).
An example
Nine seconds before detonation, with one attacker still nearby. You start the defuse, reach the halfway point and stop: they swing out to stop you and you kill them. Now you only need 3.5 seconds to finish, and you still have enough time.