Breach and clear
Breach and clear is the name for a common tactical room clearing method. It is used when capturing a room or area with guards, enemies, or hostile civilians near the entrances to the area. An explosive charge such as C4 or another similar device is placed over the door / entrance, then detonated. This allows free movement inside a heavily guarded area, as nearly all conventional locks would be destroyed by the explosion.
Breach and Clear can also be executed by opening a door first, then throwing an explosive similar to a grenade inside. This can be performed with a smoke grenade or a flashbang in order to incapacitate the enemy. This is often called smoke & clear, frag & clear, or flash (or bang) & clear.