Shield neutralizer

From Memory Alpha, the free Star Trek reference.

The shield neutralizer was a type of weapon used by the Borg Collective in the 24th century, firing small energy bursts specifically designed to drain the shields of enemy vessels. Unlike most of the Borg arsenal, this weapon affected enemy shielding only and did not appear to damage infrastructure or other systems once a shield had been dropped.

In 2365, during the chase that ensued following the first contact with the Borg, the USS Enterprise-D sustained three direct shield neutralizer hits which left her defenseless. The Borg were then able to target the nacelles, causing Enterprise to drop out of warp. (TNG: "Q Who")