This creates a bomb target where the bomb can be planted by a Terrorist that is dependent on the dimensions of the brush. The brush does not have to touch the floor but the player must at least be touching it. If there is a bomb target in your map then one of the terrorists will spawn with a bomb when each round begins (creating a defuse map type). This entity is more powerful than info_bomb_target because you can create the brush to specify the exact dimensions of the area you can plant in a bombsite and you have the ability to trigger events on bomb explosion.
Target (target) - When the bomb explodes, this entity will be triggered. This is useful for triggering things like nearby func_breakable entities or other effects.
With a successful bomb explosion the target gets fired slightly before the actual explosion effect. There is no "delay before trigger" field so it is a good idea to use a multi_manager or trigger_relay to add the desired amount of delay to get the effect you want to look right. It is a good idea to make sure the bomb cannot be planted in water (even if the brush isn't over water, it's possible the player could still be touching the brush and plant the bomb in water or drop it off an edge into water on plant). The bomb will not explode when the timer runs down if it is in water.