Glossary
Denial
In one line: Using utility to stop the enemy from doing one specific thing: crossing, defusing, planting.
What it means
Denial means denying the enemy an action: a molly on the spike to stop the defuse, a smoke or a wall to stop them crossing a choke, a trap that makes a route dangerous. It does not have to kill: it takes away time or options.
It is mostly a post-plant concept and a delaying tool on defense. The right question is "what do I want to stop them doing, and for how long?". Denial utility used too early runs out and leaves the team exposed when it really matters.
An example
You planted and a defender is about to defuse behind cover. You throw a molly on the spike: they have to stop or burn. Those lost seconds, with the spike ticking, can decide the round.