In common usage, a butter knife may refer to any table knife designed with a dull edge and rounded point; formal flatware patterns make a distinction between such a place knife (or table knife) and a butter knife. In this usage, a butter knife (or master butter knife) is a sharp-pointed, dull edged knife, often with a sabre shape, used only to serve out pats of butter from a central butter dish to individual diners' plates. Master butter knives are not used to spread the butter onto bread: this would contaminate the butter remaining in the butter dish when the next pat of butter was served. Rather, diners at the breakfast, the luncheon, and the informal dinner table use an individual butter knife to apply butter to their bread. Individual butter knives have a round point, so as not to tear the bread, and are sometimes termed butter spreaders. If no butter spreaders are provided, a dinner knife may be used an an alternative. No butter plate or butter knife appears on a really formal table as breads are placed directly on the tablecloth in a napkin to the left of the place plate.
The notch in the butter knife is there so that the user can scrape clean the edge of his or her bread piece. 
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