There are a few distinctions here. First off, a ‘single malt’ contains the distillate of one distillery alone. The less common ‘vatted malt’ designation is a bottling containing the distillate of two or more distilleries.
Second, there is difference between a single malt and a blend. The latter type contains both malt whisky (distilled in a pot still) and grain whisky (distilled in a patent still). A pot still typically offers higher quality distillate but is more expensive to run.
Third, the term ‘single malt’ is often taken as a marker of quality. Strictly speaking, though, the term is descriptive rather than evaluative. Equally, there are many top class blends. Broadly speaking, the better blends are better because they contain a high ratio of malt whisky (from several distilleries).
Fourth, the term ‘single pot still’ has appeared in recent years as regards Irish whiskey. Single pot stills are essentially the same as single malts, in that both types consist solely of pot still-derived malt whisk(e)y. The difference lies in how the barley is treated before distillation. Whereas single malts are made entirely of malted barley, single pot stills are made from a mixture of malted and unmalted barley. Malted barley is barley that has been moistened and dried before distillation commences. Unmalted barley is barley used in its natural state.
By the way, there is a flavour spectrum perceived as specific to Irish pot still. This spectrum ranges from honey to linseed oil to menthol. These flavours, fostered when the pot still is mainly casked in former bourbon barrels or virgin oak barrels, are believed to derive from unmalted barley.