A repulsorlift jammer was a device that was capable of negating the repulsorlift fields of surface vehicles. When active, the jammer would essentially cause enemy repulsorcraft to be stuck to the ground, unable to move. The Zann Consortium was known to make use of these types of devices as defensive emplacements during the height of the Galactic Civil War.
The Alliance to Restore the Republic during the Galactic Civil War was unable to afford repulsorlift jammers unlike the Galactic Empire, with General Carlist Rieekan later expressing surprise that the Empire hadn't deployed them regularly against them in the Imperial Handbook: A Commander's Guides entry on the Imperial-class 1-H repulsortank.