ROPs = Raster OPerators
TMUs= Texture Management Units
ROPs are responsible for drawing the final frame to your monitor, more ROPs usually equals higher resolutions available (not always strictly true).
TMUs are responsible for applying texels to a surface in a 3d render, more TMUs usually equals higher resolution textures (not always the case)
You can use the number of ROPs multiplied by the clock speed of the GPU to calculate pixel fill rate (how many pixels can be drawn per second, GCN GPUs draw 2 pixels per clock)
You can use the number of TMUs multiplied by the clock speed of the GPU to calculate texel fill rate (how many texels can be drawn per second)
These calculations can give you an indication of how powerful a particular GPU is, although fill rates are less important in 2016 than overall shader performance which isn't really something you can work out yourself.