What is bracketing. It is changing the exposure up and/or down to get several exposures of essentially the same subject with the same lighting.
Difficult lighting is a situation where the photographer and/or meter cannot determine the single best exposure. Best is the one the photographer wants. There may be times when the difference between the high values and low values are greater than the camera can record. I don't think these as really difficult lighting situations as much as lighting situations that are well understood, but require some tradeoffs of alternate solutions to get the print you want.
Metering is measuring the light and determing an exposure value. The photographer can use a hand held meter or thru-the-lens meter, spot meter averagpng meter or a blend. Bracketing is taking multiple exposures, sometimes based on a metered value, in the hopes of getting the exposure(s) the photographer wants.
I think of metering like a rifle and bracketing like a shot gun.