For a CNC lathe the G98 code word toggles the feedrate to inches per minute as opposed to inches per revolution with G99. If feed per minute mode is ON then the F word in any block will be read in inches per minute.

For example G98 G01 X1Z1 F2 will feed the tool at 2 inches per minute.

Compare this with G99 G01 X1Z1 F.02 which will feed the tool at .020 per revolution.