One of luther's main arguements agains the catholic church was the selling of "pardons" for sins. what were these "pardons" called?

Those pardons were called 'indulgences.'

After defeating a Confederate force near Jackson, Grant turned back to Vicksburg. On May 16, he defeated a force under General John C. ... Pemberton retreated back to Vicksburg, and Grant sealed the city by the end of May. In three weeks, Grant's men marched 180 miles, won five battles and captured some 6,000 prisoners.