The Collaborative International Dictionary
Ricochet \Ric`o*chet"\, n. [F.] A rebound or skipping, as of a ball along the ground when a gun is fired at a low angle of elevation, or of a fiat stone thrown along the surface of water.
Ricochet firing (Mil.), the firing of guns or howitzers, usually with small charges, at an elevation of only a few degrees, so as to cause the balls or shells to bound or skip along the ground.
Wikipedia
Ricochet firing is the firing of artillery at a low angle and non-maximal power so as to cause the shells to skip across the ground.
In traditional artillery tactics, either a cannon, a howitzer or occasionally a mortar would fire a shot that would just clear the outer parapet of a fortification, and then would bounce or ricochet inside the fortification's bounds. One of the primary purposes of Ricochet Fire was to dismount artillery and guns positioned on an enemy's fortifications. Additionally, Ricochet fire could also be used to cause chaos behind an enemy army's fortifications, as the ricocheting cannonball would devastate logistical structures not fortified to withstand cannon fire.
The first European use of ricochet fire (tir à ricochet) has been accredited to the Marquis de Vauban during the siege of Philippsburg in 1688. He perfected it at the siege of Ath in 1697, although it is noted that Turkish artillery divisions were using ricochet fire as early as 1608.