a penetration of an enemy's defense in depth and strength.

A means of penetrating the enemy position. This can be done by a pawn break or by a sacrifice involving pieces or pawns.

a penetration of a barrier such as an enemy's defense

Penetrating the enemy's position, whether by a pawn break or the sacrifice of pieces or pawns.

the breaching of an apparently secure formation, often with sacrifice of material, as in the Pillsbury-Lasker game in the French Defence.