hamburger icon: originally, in older Android UI guidelines, provides access to a list of items that can be used to navigate between parts of a large UI. But at this point, pretty much evolved to mean "click to access a menu" on UIs that don't have a menu bar.
Three vertical dots: "More stuff that doesn't fit on a toolbar because the display on your current device isn't wide enough".
Three horizontal dots: click this item to access a dialog.
Point-down triangle: Select an value from a list.
There may be slight variations depending on the UI guidelines for the platform you are using (or designing for).
All enormously useful icons that provide specific context and meaning. I can't say that I've ever seen a piece of serious software that abuses those conventions.
Three vertical dots: "More stuff that doesn't fit on a toolbar because the display on your current device isn't wide enough".
Three horizontal dots: click this item to access a dialog.
Point-down triangle: Select an value from a list.
There may be slight variations depending on the UI guidelines for the platform you are using (or designing for).
All enormously useful icons that provide specific context and meaning. I can't say that I've ever seen a piece of serious software that abuses those conventions.