PROC REG and PROC GLM each produce an output object named ParameterEstimates. Because the data set definition persists when the procedure ends, ODS creates a data set from each one. 
proc reg data=iron;
   model loss=fe;
title 'Parameter Estimate from PROC REG';
run;
quit;

proc glm data=iron;
   model loss=fe;
title 'Parameter Estimate from PROC GLM';
run;
quit;