ContourPlot

ContourPlot[f,{x,xmin,xmax},{y,ymin,ymax}] generates a contour plot of f as a function of x and y. 

ContourPlot[f==g,{x,xmin,xmax},{y,ymin,ymax}] plots contour lines for which f=g. 

ContourPlot[{f1==g1,f2==g2,…},{x,xmin,xmax},{y,ymin,ymax}] plots several contour lines. 

ContourPlot[…,{x,y}∈reg] takes the variables {x,y} to be in the geometric region reg. 

Please visit the official Wolfram Language Reference for more details and examples on core symbols.